The units may be found either by looking under the category in which they are used [such as length, mass, density, energy etc.], or else by picking one unit from an alphabetically ordered list of units. There are NO units of currency.There is an outline of the S I; a list of its basic defining standards and also some of its derived units; then another list of all the S I prefixes and some notes on conventions of usage.There is a short historical note on measures generally; descriptions of the Metric system, the U K (Imperial) system with a statement on the implementation of 'metrication' in the U K, and the U S system.Finally there is a list of other sources concerned with the topic of measures and units (including other Web sites) and also some notes about this document.
| Length | Area | Volume | Mass | Temperature |
| Density | Pressure & Stress |
Speed | Fuel Consumption |
Power |
| or ONE calculator just for Changing Prefixes | ||||
| Energy (Work) |
Specific Energy by Mass |
Specific Energy by Volume |
Force | Torque |
| Flow Rate by Mass |
Flow Rate by Volume |
Spread Rate by Mass (inc. Rainfall) |
Spread Rate by Volume (inc. Rainfall) |
Concentration |
| Line Density (inc. Textiles) |
Area Density | Viscosity Dynamic |
Viscosity Kinematic |
Acceleration |
| There is a Selection of Other Calculators also available | ||||
| To change . . | into . . | do this . . | To change . . | into . . | do this . . | |
| acres | hectares | x 0.4047 | kilograms | ounces | x 35.3 | |
| acres | sq. kilometres | / 247 | kilograms | pounds | x 2.2046 | |
| acres | sq. metres | x 4047 | kilograms | tonnes | / 1000 # | |
| acres | sq. miles | / 640 # | kilograms | tons (UK/long) | / 1016 | |
| barrels (oil) | cu.metres | / 6.29 | kilograms | tons (US/short) | / 907 | |
| barrels (oil) | gallons (UK) | x 34.97 | kilometres | metres | x 1000 # | |
| barrels (oil) | gallons (US) | x 42 # | kilometres | miles | x 0.6214 | |
| barrels (oil) | litres | x 159 | litres | cu.inches | x 61.02 | |
| centimetres | feet | / 30.48 # | litres | gallons (UK) | x 0.2200 | |
| centimetres | inches | / 2.54 # | litres | gallons (US) | x 0.2642 | |
| centimetres | metres | / 100 # | litres | pints (UK) | x 1.760 | |
| centimetres | millimetres | x 10 # | litres | pints (US liquid) | x 2.113 | |
| cubic cm | cubic inches | x 0.06102 | metres | yards | / 0.9144 # | |
| cubic cm | litres | / 1000 # | metres | centimetres | x 100 # | |
| cubic cm | millilitres | x 1 # | miles | kilometres | x 1.609 | |
| cubic feet | cubic inches | x 1728 # | millimetres | inches | / 25.4 # | |
| cubic feet | cubic metres | x 0.0283 | ounces | grams | x 28.35 | |
| cubic feet | cubic yards | / 27 # | pints (UK) | litres | x 0.5683 | |
| cubic feet | gallons (UK) | x 6.229 | pints (UK) | pints (US liquid) | x 1.201 | |
| cubic feet | gallons (US) | x 7.481 | pints (US liquid) | litres | x 0.4732 | |
| cubic feet | litres | x 28.32 | pints (US liquid) | pints (UK) | x 0.8327 | |
| cubic inches | cubic cm | x 16.39 | pounds | kilograms | x 0.4536 | |
| cubic inches | litres | x 0.01639 | pounds | ounces | x 16 # | |
| cubic metres | cubic feet | x 35.31 | ||||
| ____________ | ____________ | ______________ | _____________ | _____________ | __________ | |
| To change . . | into . . | do this . . | To change . . | into . . | do this . . | |
| square cm | sq. inches | x 0.1550 | ||||
| feet | centimetres | x 30.48 # | square feet | sq. inches | x 144 # | |
| feet | metres | x 0.3048 # | square feet | sq. metres | x 0.0929 | |
| feet | yards | / 3 # | square inches | square cm | x 6.4516 # | |
| fl.ounces (UK) | fl.ounces (US) | x 0.961 | square inches | square feet | / 144 # | |
| fl.ounces (UK) | millilitres | x 28.41 | square km | acres | x 247 | |
| fl.ounces (US) | fl.ounces (UK) | x 1.041 | square km | hectares | x 100 # | |
| fl.ounces (US) | millilitres | x 29.57 | square km | square miles | x 0.3861 | |
| gallons | pints | x 8 # | square metres | acres | / 4047 | |
| gallons (UK) | cubic feet | x 0.1605 | square metres | hectares | / 10 000 # | |
| gallons (UK) | gallons (US) | x 1.2009 | square metres | square feet | 10.76 | |
| gallons (UK) | litres | x 4.54609 # | square metres | square yards | x 1.196 | |
| gallons (US) | cubic feet | x 0.1337 | square miles | acres | x 640 # | |
| gallons (US) | gallons (UK) | x 0.8327 | square miles | hectares | x 259 | |
| gallons (US) | litres | x 3.785 | square miles | square km | x 2.590 | |
| grams | kilograms | / 1000 # | square yards | square metres | 1.196 | |
| grams | ounces | / 28.35 | tonnes | kilograms | x 1000 # | |
| hectares | acres | x 2.471 | tonnes | tons (UK/long) | x 0.9842 | |
| hectares | square km | / 100 # | tonnes | tons (US/short) | x 1.1023 | |
| hectares | square metres | x 10000 # | tons (UK/long) | kilograms | x 1016 | |
| hectares | square miles | / 259 | tons (UK/long) | tonnes | x 1.016 | |
| hectares | square yards | x 11 960 | tons (US/short) | kilograms | x 907.2 | |
| inches | centimetres | x 2.54 # | tons (US/short) | tonnes | x 0.9072 | |
| inches | feet | / 12 # | yards | metres | x 0.9144 # |
It is based upon 7 principal units, 1 in each of 7 different categories -
Category Name Abbreviation Length metre m Mass kilogram kg Time second s Electric current ampere A Temperature kelvin K Amount of substance mole mol Luminous intensity candela cd
Definitions of these basic units are given. Each of these units may take a prefix. From these basic units many other units are derived and named.
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Note that prefixes may be used in conjunction with any of the above units.
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The S I allows the sizes of units to be made bigger or smaller by the use of appropriate prefixes. For example, the electrical unit of a watt is not a big unit even in terms of ordinary household use, so it is generally used in terms of 1000 watts at a time. The prefix for 1000 is kilo so we use kilowatts[kW] as our unit of measurement. For makers of electricity, or bigger users such as industry, it is common to use megawatts[MW] or even gigawatts[GW]. The full range of prefixes with their [symbols or abbreviations] and their multiplying factors which are also given in other forms is
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There are various rules laid down for the use of the SI and its units as well as some observations to be made that will help in its correct use.
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In England units of measurement were not properly standardised until the 13th century, though variations (and abuses) continued until long after that. For example, there were three different gallons (ale, wine and corn) up until 1824 when the gallon was standardised.
In the U S A the system of weights and measured first adopted was that of the English, though a few differences came in when decisions were made at the time of standardisation in 1836. For instance, the wine-gallon of 231 cubic inches was used instead of the English one (as defined in 1824) of about 277 cubic inches. The U S A also took as their standard of dry measure the old Winchester bushel of 2150.42 cubic inches, which gave a dry gallon of nearly 269 cubic inches.
Even as late as the middle of the 20th century there were some differences in UK and US measures which were nominally the same. The UK inch measured 2.53998 cm while the US inch was 2.540005 cm. Both were standardised at 2.54 cm in July 1959, though the U S continued to use 'their' value for several years in land surveying work - this too is slowly being metricated.
In France the metric system officially started in June 1799 with the declared intent of being 'For all people, for all time'. The unit of length was the metre which was defined as being one ten-millionth part of a quarter of the earth's circumference. The production of this standard required a very careful survey to be done which took several years. However, as more accurate instruments became available so the 'exactness' of the standard was called into question. Later efforts were directed at finding some absolute standard based on an observable physical phenomenon. Over two centuries this developed into the S I. So maybe their original slogan was more correct than anyone could have foreseen then.
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1 yard = 0.9144 metres - same as US
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There have been three major Weights and Measures Acts in recent times (1963, 1976 and 1985) all gradually abolishing various units, as well re-defining the standards. All the Apothecaries' measures are gone, and of the Troy measures, only the ounce remains. Currently legislation has decreed that -
From the 1st October 1995, for economic, public health, public safety and administrative
purposes, only metric units are allowed EXCEPT that -
The following may continue to be used WITHOUT time limit -
That is how the legislation is framed. In common usage the 'old' units are still very apparent.
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1 yard = 0.9144 metres - same as UK
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N - O - PQ - R - S - T - UVW - XYZ
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The S I unit of length is the metre. To change any of these other units of length into their equivalent values in metres use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy. Where some uncertainty is indicated it means that a good idea of the size of the unit can be given but that a better value would depend upon knowing the period and/or culture in which the unit was being used.
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The S I unit of area is the square metre. To change any of these other units of area into their equivalent values in square metres use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy. Where some uncertainty is indicated it means that a good idea of the size of the unit can be given but that a better value would depend upon knowing the period and/or culture in which the unit was being used.
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The S I unit of volume is the cubic metre. However, this seems to be much less used than the litre (1000 litres = 1 cubic metre).To change any of these other units of volume into their equivalent values in litres use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy. The S I unit of mass is the kilogram. To change any of these other units of mass into their equivalent values in kilograms use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy.
There have been five main temperature scales, each one being named after the person who invented it. Line density is a measure of mass per unit length. The S I compatible unit of line density is kilograms/metre. A major use of line density is in the textile industry to indicate the coarseness of a yarn or fibre. For that purpose the SI unit is rather large so the preferred unit there is the tex. (1 tex = 1 gram/kilometre) To change any of these other units of line density into their equivalent values in kilograms/metre use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy.
Density is the shortened term generally used in place of the more accurate description volumetric density.It is a measure of mass per unit volume. The S I compatible unit of density is kilograms/cubic metre. However, this a rather large unit for most purposes (iron is over 7000, wood is about 600 and even cork is over 200). A much more useful size of unit is kilograms/litre (for which the previous values then become 7, 0.6 and 0.2 respectively). This unit also has the great advantage of being numerically unchanged for grams/cubic centimetre and tonnes/cubic metre (or megagrams/cubic metre). To change any of these other units of density into their equivalent values in kilograms/litre use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy.
The S I unit of energy or work is the joule. To change any of these other units of energy or work into their equivalent values in joules use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy.
The S I unit of force is the newton. To change any of these other units of force into their equivalent values in newtons use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy.
Fuel consumption of any means of transport (car, aeroplane, ship etc.) that uses fuel is a measure giving the relationship between the distance travelled for an amount of fuel used. The most common example is the car where it is usually expressed (in English-speaking countries) in miles per gallon. The S I unit of power is the watt. To change any of these other units of energy or work into their equivalent values in watts use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy.
The S I unit of pressure is the pascal. The units of pressure are defined in the same way as those for stress - force/unit area. To change any of these other units of pressure (or stress) into their equivalent values in pascals use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy. Measures based on water assume a density of 1 kg/litre - a value which rarely matched in the real world, though the error is small.
The S I compatible unit of speed is metres/second. To change any of these other units of speed into their equivalent values in metres/second use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy.
The spread rate of a substance is a measure of how much of it there is covering a unit area. The 'how much' can be measured by volume or by mass. The S I compatible unit of spread rate by mass is kilograms/square metre. It is also a measure of area density (mass/unit area) and is similar to - but not the same as - pressure, which is force/unit area. For the rainfall conversions a density of 1 kg/litre has been assumed. To change any of these other units of spread rate into their equivalent values in kilograms/square metre use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy. The conversion for rainfall assumes a density of 1 kg/litre which is accurate enough for all practical purposes.
The spread rate of a substance is a measure of how much of it there is covering a unit area. The 'how much' can be measured by volume or by mass. The S I compatible unit of spread rate by volume is cubic metres/square metre. However, this is a rather large unit for most purposes and so litres/square metre is often preferred. To change any of these other units of spread rate into their equivalent values in litres/square metre use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy.
The S I compatible unit of torque is the newton metre. To change any of these other units of torque into their equivalent values in newton metres use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy.
Conversion Tables of Units for Science and Engineering The Dent Dictionary of Measurement The Economist Desk Companion The Encyclopaedia Britannica World Weights and Measures British Weights and Measures The World of Measurements Scientific Unit Conversion
The first to be considered must the Official SI Web-site in France.
In the UK a very good place to make a start is the Metrication Resource Site run by Chris Keenan.
In the USA the National Institute of Standards and Technology (NIST) is excellent, and there is no shortage of information concerning units and their conversion. There is even an excellent 86-page book on the subject (SP 811) which can be read on-line or downloaded and printed out - but note that Adobe Acrobat Reader is needed.
An excellent A to Z of units is available from this site run by Russ Rowlett at the University of North Carolina.
Another account of metrication and associated items which has, in addition, some very good pages on historic measures (Anglo-Saxon, Biblical etc.) is provided by Jack Proot (in Canada)
The International Standards Organisation] [I S O] based in Switzerland, is responsible for the world-wide publication of standards for just about anything for which standards can be set. Whilst none of the actual data is online, details of the work of ISO and the publications they produce are. They also give many references to other organisations concerned with standards.
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Queries, comments and (further) corrections will be welcomed by Frank Tapson
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The Prefixes of the S I
yotta [Y] 1 000 000 000 000 000 000 000 000 = 10^24
zetta [Z] 1 000 000 000 000 000 000 000 = 10^21
exa [E] 1 000 000 000 000 000 000 = 10^18
peta [P] 1 000 000 000 000 000 = 10^15
tera [T] 1 000 000 000 000 = 10^12
giga [G] 1 000 000 000 (a thousand millions = a billion)
mega [M] 1 000 000 (a million)
kilo [k] 1 000 (a thousand)
hecto [h] 100
deca [da]10
1
deci [d] 0.1
centi [c] 0.01
milli [m] 0.001 (a thousandth)
micro [µ] 0.000 001 (a millionth)
nano [n] 0.000 000 001 (a thousand millionth)
pico [p] 0.000 000 000 001 = 10^-12
femto [f] 0.000 000 000 000 001 = 10^-15
atto [a] 0.000 000 000 000 000 001 = 10^-18
zepto [z] 0.000 000 000 000 000 000 001 = 10^-21
yocto [y] 0.000 000 000 000 000 000 000 001 = 10^-24
[µ] the symbol used for micro is the Greek letter known as 'mu'
Nearly all of the S I prefixes are multiples or sub-multiples of 1000. However, these are inconvenient for many purposes and so hecto, deca, deci, and centi are also used.
deca also appears as deka [da] or [dk] in the USA and Contintental Europe. So much for standards!
Conventions of Usage in the S I
A Brief History of Measurement
One of the earliest types of measurement concerned that of length. These measurements were usually based on parts of the body. A well documented example (the first) is the Egyptian cubit which was derived from the length of the arm from the elbow to the outstretched finger tips. By 2500 BC this had been standardised in a royal master cubit made of black marble (about 52 cm). This cubit was divided into 28 digits (roughly a finger width) which could be further divided into fractional parts, the smallest of these being only just over a millimetre.
Metric System of Measurements
Length Area
10 millimetres = 1 centimetre 100 sq. mm = 1 sq. cm
10 centimetres = 1 decimeter 10 000 sq. cm = 1 sq. metre
10 decimetres = 1 metre 100 sq. metres = 1 are
10 metres = 1 decametre 100 ares = 1 hectare
10 decametres = 1 hectometre 10 000 sq. metres = 1 hectare
10 hectometres = 1 kilometre 100 hectares = 1 sq. kilometre
1000 metres = 1 kilometre 1 000 000 sq. metres = 1 sq. kilometre
Volume Capacity
1000 cu. mm = 1 cu. cm 10 millilitres = 1 centilitre
1000 cu. cm = 1 cu. decimetre 10 centilitree = 1 decilitre
1000 cu. dm = 1 cu. metre 10 decilitres = 1 litre
1 million cu. cm = 1 cu. metre 1000 litres = 1 cu. metre
Mass
1000 grams = 1 kilogram
1000 kilograms = 1 tonne
The distinction between 'Volume' and 'Capacity' is artificial and kept here only for historic reasons.
A millitre is a cubic centimetre and a cubic decimetre is a litre.
But see under 'Volume' for problems with the litre.
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The U K (Imperial) System of Measurements
Length Area
12 inches = 1 foot 144 sq. inches = 1 square foot
3 feet = 1 yard 9 sq. feet = 1 square yard
22 yards = 1 chain 4840 sq. yards = 1 acre
10 chains = 1 furlong 640 acres = 1 square mile
8 furlongs = 1 mile
5280 feet = 1 mile
1760 yards = 1 mile Capacity
20 fluid ounces = 1 pint
Volume 4 gills = 1 pint
1728 cu. inches = 1 cubic foot 2 pints = 1 quart
27 cu. feet = 1 cubic yard 4 quarts = 1 gallon (8 pints)
Mass (Avoirdupois)
437.5 grains = 1 ounce Troy Weights
16 ounces = 1 pound (7000 grains) 24 grains = 1 pennyweight
14 pounds = 1 stone 20 pennyweights = 1 ounce (480 grains)
8 stones = 1 hundredweight [cwt] 12 ounces = 1 pound (5760 grains)
20 cwt = 1 ton (2240 pounds)
Apothecaries' Measures Apothecaries' Weights
20 minims = 1 fl.scruple 20 grains = 1 scruple
3 fl.scruples = 1 fl.drachm 3 scruples = 1 drachm
8 fl.drachms = 1 fl.ounce 8 drachms = 1 ounce (480 grains)
20 fl.ounces = 1 pint 12 ounces = 1 pound (5760 grains)
The old Imperial (now UK) system was originally defined by three standard measures - the yard, the pound and the gallon which were held in London. They are now defined by reference to the S I measures of the metre, the kilogram and the litre. These equivalent measures are exact.
1 pound = 0.453 592 37 kilograms - same as US
1 gallon = 4.546 09 litres
Note particularly that the UK gallon is a different size to the US gallon so that NO liquid measures of the same name are the same size in the UK and US systems.
Also that the ton(UK) is 2240 pounds while a ton(US) is 2000 pounds. These are also referred to as a long ton and short ton respectively.
Metrication in the U K
may be used until 31st December 1999.
Sports are exempt from all of this, but most of them have (voluntarily) changed their relevant regulations into statements of equivalent metric measures.
Historical Perspectives on Metrication by Jim Humble
who was the last Director of the UK Metrication Board.
The first parliamentary reference to metrication in the UK was 13th April 1790. This was when parliamentarian Sir John Riggs Miller [Britain] and the Bishop of Autum, Prince Talleyrand [France] put to the British Parliament and French Assembly respectively, the proposition that the two countries should cooperate to equalise their weights and measures, by the joint introduction of the metric system.
There was no immediate progress although there were many positive debates in the second half of the 19th Century. For example, 1st July 1863 the Bill for a compulsory change to the metric system was approved by 110 votes to 75 votes. Speakers argued many of the points we hear today. On the one hand supporters argued its logic and simplicity, savings in time and money, advantages to trade and education. Opponents stressed the undesirability of following the precedent of France and the problems of conversion for the illeducated and disadvantaged. However no specific cut-off dates were proposed.
The following year, 9th March 1864, the House of Lords debated a Bill to permit the use of metric weights and measures in trade. One supporter noted that Englishmen were notorious for liking old terms and old habits and he hoped that the new nomenclature would not be diverted by attempts at ridicule. He said the sound of the word 'metric' can be absurd to anyone but a fool who has never heard it before; but no more than a 'yard' to a man who has never heard of a 'yard' before.... !!! Parliament passed the Bill and this became the Metric Weights and Measures Act 1864.
On the 24th February 1868 a parliamentary proposal to set Imperial cut-off dates was withdrawn on promise of a Royal Commission of enquiry. The Enquiry Report was positive, and on the 26th July 1871 Britain almost became a metric country. The government lost the Bill to make metric compulsory after two years, by only 82 votes to 77 votes. An argument that might have influenced opponents was a plea that Britain would be "letting down America and our colonies" who had harmonised their systems with the ones in use in Britain. [NB At that time the American Congress had emulated Britain by allowing contracts in metric. A particularly strong USA advocate for metric was John Quincy Adams.]
There were further debates, and near misses, in the UK Parliament in 1872 and 1896, before a comprehensive debate [21st June - 6th August 1897] concluded by legalising the use of metric for all purposes. There were no contrary votes. [NB This is the debate which most references indicate to be the genesis of metrication in the United Kingdom.]
Metrication continued to be debated for the next 10 years. In 1904 The House of Lords unanimously voted to make metric compulsory after two years. It was claimed that the Austrian and German nations had successfully made metric compulsory with a changeover time of only "one week"!!!!! . The Government said they would not obstruct the proposal, but the Bill
was never adopted in the Commons. Two similar debates in 1907 failed. By now, the Board of Trade was expressing some reservations, claiming that metrication had failed in France and that the agricultural labourer would never ask for 0.56825 of a litre of beer. The vote against compulsion rose to 150 votes to 118 votes. Conflicts in Europe put further political consideration of metrication out of mind until the publication of a Government White Paper on Weights and Measures 10th May 1951.
The 1951 White Paper was in fact the 28th Report put to Parliament during the preceeding 100 years. This latest report was in response to the the Hodgson Committee Report published in 1949. Eventually we had the Weights and Measures Act 1963; a long series of Parliamentary questions to Ministers and the Federation of British Industries [now the CBI] lobby in favour of metrication in 1965. These initiatives culminated with the creation of the Metrication Board in 1969 by Anthony Wedgewood Benn, Minister of Technology. The target date for completion was end 1975. The transition to metrication and the role of the Board were given positive support and encouragement by Geoffrey Howe the responsible Minister of the new Government in 1972. Indeed at that time, and until circa 1977/8, there was good, sensible and
steady progress which seemed to be supported by every section of society including, for example, the small retailers and the elderly as represented by Age Concern.
Prepackaged food changed but the really difficult issue to emerge affected retailers of 'loose weight' products. They needed to be reassured there would be an agreed cut-off date for their transfer from Imperial to metric. The retail problem was that metric prices would always appear to be more expensive than their nearest Imperial equivalent.
Voluntary transferees to metric found themselves commercially disadvantaged. This is because viz. 4 ozs is smaller than 125 g: one pound is smaller than 500 g and a pint is smaller than a litre. Prices are correspondingly lower. The issue of how best to explain the position to consumers dominated much of the Board's creative thinking.
The product which brought all voluntary retail initiatives to a full stop was the experience of the floor covering and carpet retailers. Their 1975 change to sales by the sq. metre started well, but in 1977 one of the major High Street retailers found enormous commercial advantage in reverting to sales by the square yard. Consumers could not be persuaded to believe that goods costing, for example, £10 per square or £12 per square metre were virtually priced the same. Consumers bought, in very significant volume, the apparently cheaper priced imperial version. Metrication of carpet sales entered into full scale reverse and the Chambers of Trade and retail associations pressed for firm Government leadership i.e. compulsory cut-off. With hindsight one of the Metrication Board jingles may have helped spread the 'carpet' misunderstanding. This was the jingle " a metre measures about three foot three, just a bit longer than a yard you see". Consumers understandably couldn't relate an e.g. £2 per square unit price difference with the Metrication Board's "just a bit longer". Then the political nerve began to fail.
Board of Trade Ministers Shirley Williams, Alan Williams and later Roy Hattersley and John Fraser supported metrication. They seemed to recognise the setting of a cut-off date was unavoidable. They had had, by this time, the benefit of analysing the results of successful metric changes in all the Commonwealth countries. There was a wealth of
information within the Department of Trade to show that a clear retail cut-off date was both desirable and inevitable....exactly as 19th Century parliamentarians had forseen. The necessary Order, drafted by the Board of Trade in 1978, was agreed by a huge range of retail trade, industry, engineering, consumer, trade union, elderly person, sporting
and educational organisations and..... the overwhelming number of parliamentarians. A small number of critics, in each political party, did voice opposition to the element of compulsion but this seemed to come from a relatively small minority within the Eurosceptic movement.
However, the initiative was in the hands of Secretary of State for Trade, Roy Hattersley and a General Election was expected in 1979. There seemed to be weeks and weeks of "will he/ won't he" allow Parliament to vote for the Order giving the final Imperial cut-off. Almost every private test of opinion indicated the Order would command a substantial majority in Parliament. Although the Opposition sensed a weakness in the resolution of the Labour Government it was acknowledged that many conservative MPs had been career-long advocates for cut-off and would therefore be likely to favour the Government Order, or at least abstain. In the event, Roy Hattersley chose not to test opinion, not to allow the vote. He withdrew the draft Order. Speculation was that he judged the issue might lose some votes in the forthcoming election. Plenty of time to introduce Imperial cut-off Orders after a Labour victory. The junior Trade Minister, John Fraser, made his disgust and disappointment apparent... suggesting the actions of his Secretary of State would be seen as "gutless". Many shared that view. Labour lost the election anyway and Margaret Thatcher became Prime Minister.
One Conservative backbencher, Sally Oppenheim had been almost the lone but persistent critic of the metric programme. Ironically she was appointed junior Minister of Consumer Affairs at the DTI and then metrication was added to her portfolio. In letters to MP's and associations she made it clear
[a] she was not opposed the metrication in principle,
[b] metrication was not the result of Britain's accession to the EEC but
[c] she did object to measures which would compel people to adopt metric against their will. Proponents of metrication, trade and consumer organisations, officials and the Metrication Board explained and argued that a voluntary change at retail level was absolutely impossible...it could never happen. It was a recipe for confusion, waste and duplication. Government had to lead over the last hurdle. It did, it led backwards. In 1980 the Metrication Board was abolished.
In truth the Metrication Board had little else to do. Every possible programme had been agreed, consumer information campaigns composed and there was nothing to do until or unless a date was fixed for the completion of the transition. We little knew then the die was set for a further 20 years of waste, confusion and argument. Successive DTI Ministers did nothing to inform consumers or public opinion. They did nothing to refute the new 'big lie' namely, that Britain was being forced to change because of the European Commission. In fact, during the past 20 years most Commission Officials, European Politicians and businesses in Continental Europe 'couldn't have given a damn' whether Britain changed to the metric system or not. They seemed to quite like the idea of Britain shooting itself in its economic foot, by imposing upon itself the extra costs and waste of maintaining a dual system. For twenty years not one single British Minister has attempted to explain the advantages of metrication; been frank about the changes which had successfully taken place in the rest of the World or the fact that we had committed ourselves to become a metric nation long before we joined the European Community.
Most tried to pretend or imply they were protecting our British culture from the European bully.
How sad, what a waste, what a pity.
Jim Humble OBE
Director of the Metrication Board
[1978-1980]
Some other dates of note
1950 The Hodgson Report
was published which, after arguing all the points for and against, favoured a change to metric.
1963 Weights and Measures Act
defined the basic measures of the 'yard' and the 'pound' in terms of the 'metre' and the 'kilogram'. Many of the old imperial measures were abolished (drachm, scruple, minim, chaldron, quarter, rod, pole, perch, and a few more)
1971
Currency was Decimalised
1985 Weights and Measures Act
abolished several more imperial measures for purposes of trade, and defined the 'gallon' in terms of the 'litre'.Thus, all the measures had been metricated even if the public hadn't!
The U S System of Measurements
Most of the US system of measurements is the same as that for the UK. The biggest differences to be noted are in Capacity which has both liquid and dry measures as well as being based on a different standard - the US liquid gallon is smaller than the UK gallon. There is also a measurement known at the US survey foot. It is gradually being phased out as the maps and land plans are re-drawn under metrication. (The changeover is being made by putting 39.37 US survey feet = 12 metres)
Length Area
12 inches = 1 foot 144 sq. inches = 1 square foot
3 feet = 1 yard 9 sq. feet = 1 square yard
220 yards = 1 furlong 4840 sq. yards = 1 acre
8 furlongs = 1 mile 640 acres = 1 square mile
5280 feet = 1 mile 1 sq.mile = 1 section
1760 yards = 1 mile 36 sections = 1 township
Volume
1728 cu. inches = 1 cubic foot
27 cu. feet = 1 cubic yard
Capacity (Dry) Capacity (Liquid)
16 fluid ounces = 1 pint
2 pints = 1 quart 4 gills = 1 pint
8 quarts = 1 peck 2 pints = 1 quart
4 pecks = 1 bushel 4 quarts = 1 gallon (8 pints)
Mass
437.5 grains = 1 ounce Troy Weights
16 ounces = 1 pound (7000 grains) 24 grains = 1 pennyweight
14 pounds = 1 stone 20 pennyweights = 1 ounce (480 grains)
100 pounds = 1 hundredweight [cwt] 12 ounces = 1 pound (5760 grains)
20 cwt = 1 ton (2000 pounds)
Apothecaries' Measures Apothecaries' Weights
60 minims = 1 fl.dram 20 grains = 1 scruple
8 fl.drams = 1 fl.ounce 3 scruples = 1 dram
16 fl.ounces = 1 pint 8 drams = 1 ounce (480 grains)
12 ounces = 1 pound (5760 grains)
As with the UK system these measures were originally defined by physical standard measures - the yard, the pound, the gallon and the bushel.They are now all defined by reference to the S I measures of the metre, the kilogram and the litre. These equivalent measures are exact.
1 pound = 0.453 592 37 kilograms - same as UK
1 gallon (liquid) = 3.785 411 784 litres
1 bushel = 35.239 070 166 88 litres
Note particularly that the US gallon is a different size to the UK gallon so that NO liquid measures of the same name are the same size in the US and UK systems.
Also that the ton(US) is 2000 pounds while a ton(UK) is 2240 pounds. These are also referred to as a short ton and long ton respectively.
Note than in matters concerned with land measurements, for the most accurate work, it is necessary to establish whether the US survey measures are being used or not.
Categories of Units
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List of Units
The units are listed in alphabetical order but scanning can be speeded up by selecting the initial letter of the unit from these individual letters or groups
A - B - C - D - E - F - G - H - IJ - K - L -
M
A
B
C
D
E
F
G
H
IJ
K
L
M
N
O
PQ
R
S
T
UVW
XYZ
Length
angstroms divide by 10 000 000 000 #
astronomical units x 149 598 550 000
barleycorns x 0.008 467
centimetres x 0.01 #
chains (surveyors') x 20.1168 #
cubits x (0.45 to 0.5)
ells (UK) x 0.875 (but many variations)
ems (pica) x 0.004 233 3
fathoms x 1.8288 #
feet (UK and US) x 0.3048 #
feet (US survey) x 0.304 800 609 6
furlongs x 201.168 #
hands x 0.106 #
inches x 0.0254 #
kilometres x 1000 #
leagues x (4000 to 5000)
light years x 9 460 500 000 000 000
links (surveyors') x 0.201 168 #
metres [m] 1
microns (=micrometres) x 0.000 001 #
miles (UK and US) x 1609.344 #
miles (nautical) x 1852 #
parsecs x 30 856 770 000 000 000
perch (=rods or poles) x 5.0292 #
picas (computer) x 0.004 233 333
picas (printers') x 0.004 217 518
points (computer) x 0.000 352 777 8
points (printers') x 0.000 351 459 8
yards x 0.9144 #
Note than in matters concerned with land measurements, for the most accurate work, it is necessary to establish whether the US survey measures are being used or not.
Area
acres x 4046.856 422 4 #
ares x 100 #
circular inches x 0.000 506 707 479
hectares x 10 000 #
hides x 485 000 (with wide variations)
roods x 1011.714 105 6 #
square centimetres x 0.000 1 #
square feet (UK and US) x 0.092 903 04 #
square feet (US survey) x 0.092 903 411 613
square inches x 0.000 645 16 #
square kilometres x 1 000 000 #
square metres 1
square miles x 2 589 988.110 336 #
square millimetres x 0.000 001 #
squares (of timber) x 9.290 304 #
square rods (or poles) x 25.292 852 64 #
square yards x 0.836 127 36 #
townships x 93 239 571.972
Note than in matters concerned with land measurements, for the most accurate work, it is necessary to establish whether the US survey measures are being used or not.
Volume or Capacity
The litre. There can be some ambiguity about the size of the litre. In 1901 it was defined by reference to a kilogram of pure water under certain particular conditions. (This was similar to the way the old UK gallon was set.) In 1964 it was re-defined as a common usage term for a cubic decimetre. They differ very slightly and for really accurate work, to avoid any possible confusion, it is recommended that the litre is not used . It is used here as being a cubic decimetre.
barrels (oil) x 158.987 294 928 #
bushels (UK) x 36.368 72 #
bushels (US) x 35.239 070 166 88 #
centilitres x 0.01 #
cubic centimetres x 0.001 #
cubic decimetres 1
cubic decametres x 1 000 000 #
cubic feet x 28.316 846 592 #
cubic inches x 0.016 387 064 #
cubic metres x 1000 #
cubic millimetres x 0.000 001 #
cubic yards x 764.554 857 984 #
decilitres x 0.1 #
fluid ounces (UK) x 0.028 413 062 5 #
fluid ounces (US) x 0.029 573 529 562 5 #
gallons (UK) x 4.546 09 #
gallons, dry (US) x 4.404 883 770 86 #
gallons, liquid (US) x 3.785 411 784 #
litres [l or L] 1
litres (1901 - 1964) x 1.000 028
millilitres x 0.001 #
pints (UK) x 0.568 261 25 #
pints, dry (US) x 0.550 610 471 357 5 #
pints, liquid (US) x 0.473 176 473 #
quarts (UK) x 1.136 522 5 #
quarts, dry (US) x 1.101 220 942 715 #
quarts, liquid (US) x 0.946 352 946 #
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Mass (or Weight)
carats, metric x 0.000 2 #
grains x 0.000 064 798 91 #
grams x 0.001 #
hundredweights, long x 50.802 345 44 #
hundredweights, short x 45.359 237 #
kilograms [kg] 1
ounces, avoirdupois x 0.028 349 523 125 #
ounces, troy x 0.031 103 476 8 #
pounds x 0.453 592 37 #
slugs (or g-pounds) x 14.593 903
stones x 6.350 293 18 #
tons (UK or long) x 1016.046 908 8 #
tons (US or short) x 907.184 74 #
tonnes x 1000 #
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Temperature
G D FAHRENHEIT (1686-1736) a German physicist, in about 1714 proposed the first practical scale. He called the freezing-point of water 32 degrees (so as to avoid negative temperatures) and the boiling-point 212 degrees.
R A F de REAUMUR (1673-1757) A French entomologist, proposed a similar scale in 1730, but set the freezing-point at 0 degrees and the boiling-point at 80 degrees. This was used quite a bit but is now obsolete.
Anders CELSIUS (1701-1744) a Swedish astronomer, proposed the 100-degree scale (from 0 to 100) in 1742. This was widely adopted as the centigrade scale. But since grades and centigrades were also measures of angle, in 1948 it officially became the Celsius scale. Also, the S I system of units gives preference to naming units after people where possible.
William Thomson, 1st Lord KELVIN (1824-1907) a Scottish mathematician and physicist, worked with J P Joule - about 1862 - to produce an absolute scale of temperature based on laws of heat rather than the freezing/boiling-points of water. This work produced the idea of 'absolute zero', a temperature below which it was not possible to go. Its value is -273.15 degrees on the Celsius scale.
William J M RANKINE (1820-1872) a Scottish engineer and scientist, promoted the Kelvin scale in its Fahrenheit form, when the equivalent value of absolute zero is -459.67 degrees Fahrenheit.
Nowadays, while scientists use the KELVIN scale, the CELSIUS scale is the preferred scale in our everyday lives. However, the Fahrenheit scale is still widely used and there frequently is a need to be able to change from one to the other.
To change temperature given in Fahrenheit (F) to Celsius (C)
Start with (F); subtract 32; multiply by 5; divide by 9; the answer is (C)
To change temperature given in Celsius (C) to Fahrenheit (F)
Start with (C); multiply by 9; divide by 5; add on 32; the answer is (F)
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Line density
denier divide by 9 000 000 #
drex divide by 10 000 000 #
grams/centimetre divide by 10 #
grams/kilometre (tex) divide by 1 000 000 #
grams/metre divide by 1000 #
grams/millimetre 1
kilograms/kilometre divide by 1000 #
kilograms/metre 1
milligrams/centimetre divide by 10 000 #
milligrams/millimetre divide by 1000 #
ounces/inch x 1.116 125
ounces/foot x 0.093 01
pounds/inch x 17.858
pounds/foot x 1.488 164
pounds/yard x 0.496 055
pounds/mile x 0.000 281 849
tex divide by 1 000 000 #
tons(UK)/mile x 0.631 342
tons(US)/mile x 0.563 698
tonnes/kilometre 1
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Density
grains/gallon(UK) divide by 70 156
grains/gallon(US) divide by 58 418
grams/cubic centimetre 1
grams/litre divide by 1000 #
grams/millilitre 1
kilograms/cubic metre divide by 1000 #
megagrams/cubic metre 1
milligrams/millilitre divide by 1000 #
milligrams/litre divide by 1 000 000 #
kilograms/litre 1
ounces/cubic inch x 1.729 994 044
ounces/gallon(UK) x 0.006 236 023
ounces/gallon(US) x 0.007 489 152
pounds/cubic inch x 27.679 904
pounds/cubic foot x 0.016 018 463
pounds/gallon(UK) x 0.099 776 373
pounds/gallon(US) x 0.119 826 427
tonnes/cubic metre 1
tons(UK)/cubic yard x 1.328 939 184
tons(US)/cubic yard x 1.186 552 843
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Energy or work
There is a lot of room for confusion in some of the units used here.
The calorie can take 5 different values and, while these do not vary by very much, for accurate work it is necessary to specify which calorie is being used.
The 5 calories are known as the International Table calorie - cal(IT); the thermochemical calorie - cal(th); the mean calorie - cal(mean); the 15 degree C calorie - cal(15C); and the 20 degree C calorie - cal(20C).
As a further complication, in working with food and expressing nutritional values, the unit of a Calorie (capital C) is often used to represent 1000 calories, and again it is necessary to specify which calorie is being used for that.
The British thermal unit (Btu) can also take different values and they are named in a similar way to the calorie, that is
British thermal units(IT)x 1055.056
Btu (th) x 1054.350
Btu (mean) x 1055.87
calories - cal (IT) x 4.1868 #
- cal (th) x 4.184 #
- cal (mean) x 4.190 02
- cal (15C) x 4.185 80
- cal (20C) x 4.181 90
Calorie (food) x 4186 (approx.)
centigrade heat units x 1900.4
ergs divide by 10 000 000 #
foot pounds-force x 1.355 817
foot poundals x 0.042 140
gigajoules [GJ] x 1000 000 000 #
horsepower hours x 2 684 520 (approx.)
joules [J] 1
kilocalories (IT) x 4186.8 #
kilocalories (th) x 4184 #
kilogram-force metres x 9.806 65 #
kilojoules [kJ] x 1000 #
kilowatt hours [kWh] x 3 600 000 #
megajoules [MJ] x 1 000 000 #
newton metres [Nm] x 1 #
therms x 105 500 000 (approx.)
watt seconds [Ws] 1
watt hours [Wh] x 3600 #
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Force
dynes divide by 100 000 #
kilograms force x 9.806 65 #
kilonewtons [kN] x 1000 #
kips x 4448.222
meganewtons [MN] x 1 000 000 #
newtons [N] 1
pounds force x 4.448 222
poundals x 0.138 255
sthenes (=kN) x 1000
tonnes force x 9806.65 #
tons(UK) force x 9964.016
tons(US) force x 8896.443
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Fuel Consumption
It could also be expressed in gallons per mile. However, for a car the latter method gives a rather small figure: 35 miles per gallon is about 0.0286 gallons per mile. In that case it would be better to give a figure for 100 miles, so it would be 2.86 gallons per 100 miles. That is the metric way of expressing fuel consumption - as litres per 100 kilometres.
From regular enquiries it appears that in real life people are using all sorts of ways of expressing their fuel consumption, so this section (unlike all the others) tries to cover as many ways as possible. All the values are given to an accuracy of 4 significant figures.
To change into
miles per gallon (UK) miles per gallon (US) multiply by 0.833
miles per gallon (UK) miles per litre multiply by 0.22
miles per litre miles per gallon (UK) multiply by 4.546
miles per gallon (UK) kilometres per litre multiply by 0.354
miles per gallon (US) miles per gallon (UK) multiply by 1.2
miles per gallon (US) miles per litre multiply by 0.2642
miles per litre miles per gallon (US) multiply by 3.785
miles per gallon (US) kilometres per litre multiply by 0.4251
X miles per gallon gallons per 100 miles: divide 100 by X
(both gallons must of the same type)
X miles per gallon (UK) litres per 100 km: divide 282.5 by X
X miles per gallon (US) litres per 100 km: divide 235.2 by X
X km per litre litres per 100 km: divide 100 by X
X miles per litre litres per 100 km: divide 62.14 by X
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Power
Since power is a measure of the rate at which work is done, the underlying units are those of work or energy, and that section should be looked at for explanations concerning the calorie and Btu. In this section the (IT) values have been used.
In this section it is the horsepower which provides confusion. Just like the calorie, it can take 5 different values, and these are identified as necessary by the addition of (boiler), (electric), (metric), (UK) and (water). Unlike the calorie (whose 5 values are reasonably close to each other), the horsepower has 4 which are close and 1 (boiler) which is considerably different - it is about 13 times bigger than the others - but it seems to be very little used.
Btu/hour x 0.293 071
Btu/minute x 17.584 267
Btu/second x 1055.056
calories/hour x 0.001 639
calories/minute x 0.069 78
calories/second x 4.1868 #
ft lb-force/minute x 0.022 597
ft lb-force/second x 1.355 82
gigawatts [GW] x 1 000 000 000
horsepower (electric) x 746 #
horsepower (metric) x 735.499
watts [W] 1
joules/hour divide by 3600 #
joules/minute divide by 60 #
joules/second 1
kilocalories/hour x 1.163
kilocalories/minute x 69.78
kg-force metres/hour x 0.002 724
kg-force metres/minute x 0.163 444
kilowatts [kW] x 1000 #
megawatts [MW] x 1 000 000 #
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Pressure or Stress
atmospheres x 101 325 #
bars x 100 000 #
centimetres of mercury x 1333.22
centimetres of water x 98.066 5 #
feet of water x 2989.066 92 #
hectopascals [hPa] x 100 #
inches of water x 249.088 91 #
inches of mercury x 3386.388
kg-force/sq.centimetre x 98 066.5 #
kg-force/sq.metre x 9.806 65 #
kilonewton/sq.metre x 1000 #
kilopascal [kPa] x 1000 #
kips/sq.inch x 6 894 760
meganewtons/sq.metre x 1 000 000 #
metres of water x 9806.65 #
millibars x 100 #
pascals [Pa] 1
millimetres of mercury x 133.322
millimetres of water x 9.806 65 #
newtons/sq.centimetre x 10 000
newtons/sq.metre 1
newtons/sq.millimetre x 1 000 000 #
pounds-force/sq.foot x 47.880
pounds-force/sq.inch x 6894.757
poundals/sq.foot x 1.448 16
tons(UK)-force/sq.foot x 107 251
tons(UK)-force/sq.inch x 15 444 256
tons(US)-force/sq.foot x 95 760
tons(US)-force/sq.inch x 13 789 500
tonnes-force/sq.cm x 98 066 500 #
tonnes-force/sq.metre x 9806.65 #
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Speed
centimetres/minute divide by 6000 #
centimetres/second divide by 100 #
feet/hour divide by 11 811
feet/minute x 0.005 08 #
feet/second x 0.3048 #
inches/minute divide by 2362.2
inches/second x 0.0254 #
kilometres/hour divide by 3.6 #
kilometres/second x 1000 #
knots x 0.514 444
Mach number x 331.5
metres/hour divide by 3600 #
metres/minute divide by 60 #
metres/second [m/s] 1
miles/hour x 0.447 04 #
miles/minute x 26.8224 #
miles/second x 1609.344 #
yards/hour divide by 3937
yards/minute x 0.015 24 #
yards/second x 0.9144 #
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Spread Rate (by mass)
grams/sq.centimetre x 10 #
grams/sq.metre divide by 1000 #
inches of rainfall x 2.54
kilograms/hectare divide by 10 000 #
kilograms/sq.centimetre x 10 000 #
milligrams/sq.metre divide by 1000 #
millimetres of rainfall 1
kilograms/sq.metre 1
ounces/sq.foot x 0.305 152
ounces/sq.inch x 43.942
ounces/sq.yard divide by 49.494
pounds/acre divide by 8921.791
pounds/sq.foot x 4.882 428
pounds/sq.inch x 703.07
pounds/sq.yard x 0.542 492
tonnes/hectare divide by 10 #
tons(UK)/acre divide by 3.982 942
tons(US)/acre divide by 4.460 896
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Spread Rate (by volume)
cubic feet/acre divide by 142.913
cubic inches/sq.yard divide by 51.024
cubic yards/sq.mile divide by 3387.577
cubic metres/hectare divide by 10 #
cubic metres/sq.km divide by 1000 #
cubic metres/sq.metre x 1000 #
fl. ounces(UK)/sq.yard divide by 29.428
litres/square metre 1
gallons(UK)/acre divide by 890.184
gallons(US)/acre divide by 1069.066
gallons(UK)/hectare divide by 2199.692
gallons(US)/hectare divide by 2641.721
inches of rainfall x 25.4 #
litres/hectare divide by 10 000 #
millilitres/sq.metre divide by 1000 #
millimetres of rainfall 1
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Torque
dyne centimetres divide by 10 000 000 #
gram-force centimetres x 0.000 098 066 5 #
kg-force centimetres x 0.098 066 5 #
kg-force metres x 9.806 65 #
newton centimetres divide by 100 #
newton metres [Nm] 1
ounce-force inches divide by 141.612
pound-force inches x 0.112 984
pound-force feet x 1.355 818
poundal feet x 0.042 140
ton(UK)-force feet x 3 037.032
ton(US)-force feet x 2 711.636
tonne-force metres x 9 806.65 #
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Other Sources in Books
by Ari L Horvath
Macmillan Reference Books, London, 1986 (147 pages)
ISBN 0 333 40857 8
Probably the most comprehensive set of conversion factors in print, covering both old and modern units. There are 77 tables covering categories from Length to Radiation dosage. The Length table alone lists 107 units together with the conversion factors needed to change each one into metres.
by Darton and Clark
J M Dent, London, 1994 (538 pages)
ISBN 0 460 861379
Very comprehensive coverage of all kinds of units (including currencies), ordered in conventional dictionary form, and giving several conversion factors.
Random Century, London, 1992 (272 pages)
ISBN 0 7126 9816 7
A handy compendium of units used in Science, Medicine, Engineering, Industry, Commerce, Finance and many other places, together with all the necessary conversion factors. There is also much other incidental (but related) information.
The modern E B has many references to units, but extensive use needs to be made of the index to find them all. It gives a wide selection of weights and measures from countries around the world and the appropriate conversion factors.
Statistical Office of the United Nations, New York 1955 (225 pages)
A very comprehensive survey of each country in the world (as it was then) from Aden to Zanzibar, giving the units used in each for Length, Area and Capacity with their British and Metric equivalents. There is an appendix on the measures used for selected commodities. Currencies are also given. The indexes are very thorough.
The Weights and Measures of England
by R D Connor
H M S O, London, 1987 (422 pages)
ISBN 0 460 86137 9
A scholarly and detailed account of the history of the development of the British (Imperial) system of weights and measures from the earliest times.
by R E Zupko
A history from Antiquity to the Seventeenth Century
The University of Wisconsin Press, 1977 [248 pages]
ISBN 0 299 07340 8
The actual history occupies only 100 pages. There is then an extensive list of the various units used in commerce, tables of many pre-Imperial units, a long list of pre-metric measures used in Europe together with their British and metric equivalents, and nearly 40 pages giving other sources.
by H Arthur Klein
Allen and Unwin, London, 1975 (736 pages)
ISBN 0 04 500024 7
A very readable and comprehensive account of the history of units used in measuring, from the earliest known beginnings and around the world.
by Francois Cardarelli
Springer-Verlag, London, 1997 (456 pages)
ISBN 3-540-76022-9
It claims "This practical manual aims to be the most comprehensive work on the subject of unit conversion. It contains more than 10 000 precise conversion factors."
It is certainly a very chunky and compact (= handy-sized) book. Comprehensive it certainly is but still not complete. However, with its very wide coverage, both historical and modern, it should certainly satisfy nearly all users.
Other Sources on the World Wide Web
The problem is simply: which one best suits the purpose?
It covers just about everything one could want to know about metrication and, if not covered, gives links to sites where you might find it. Current state of progress, legislation, directives, arguments (for and against), conversions, and many other points of interest, all get a mention.
The US Metric Association is also a good starting point which provides a wealth of links to other suitable sites.
Notes
This dictionary is not meant to be encyclopaedic in its coverage, and there are many many more units which are not touched upon, but it is hoped that all 'ordinary' needs are covered. The many references to other sources, both in books and on-line should take care of anything beyond that.
Finally, I must thank all of those who wrote with suggestions (and corrections!) after reading the earlier editions.
19th June 1995 (First placed online)
27th August 1997 (Minor corrections)
21st November 1997 (Major corrections and alterations)
20th January 1999 (Minor corrections and alterations)
9th August 1999 (A few adjustments to links)
13th December 1999 (Summary table of conversion factors added)
1st March 2000 (Some re-writing of Web section and links to first conversion calculators put in)
kumpf last updated Mar 23, 2001