The units may be found either by looking under the in which they are used, (length energy etc.) | category |
or by picking one unit from an alphabetically ordered | list of units. |
There is an outline of the | S I system, |
a list of its 7 basic | definitions, |
some of its | derived units, |
together with a list of all the | S I prefixes, |
and some of the rules and conventions for | its usage. |
On the subject of measures generally, there is a short | historical note. |
Then there are descriptions of the | Metric system, |
and the | U K (Imperial) system, |
followed by statements on the implementation of | 'metrication' in the U K, |
and then the | U S system of measures. |
At the bottom of this document is a | list of other sources, |
and also some links to other | Web sites. |
Finally there are some | notes on this material . |
Category Name Abbrev. 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 |
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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 (a hundred) deca [da]10 (ten) 1 deci [d] 0.1 (a tenth) centi [c] 0.01 (a hundredth) 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 |
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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.
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. |
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 |
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) |
1 yard = 0.9144 metres - same in US 1 pound = 0.453 592 37 kilograms - same in US 1 gallon = 4.546 09 litres - different in US |
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 now gone,
and of the Troy measures, only the ounce remains. The legislation
decreed that -
From the 1st October 1995, for economic, public health, public safety and administrative purposes, only metric units were to be allowed EXCEPT that -
The following could continue to be used WITHOUT time limit -
That was how the legislation was framed. In common usage the 'old' units are still very apparent. |
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! |
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) |
1 yard = 0.9144 metres - same as UK 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 |
Units are listed in alphabetical order. 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 N - O - PQ - R - S - T - UVW - XYZ |
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 0.1016 # 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 # |
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 |
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 # |
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 # |
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) |
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 |
grains/gallon(UK) divide by 70 157 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 27.679 905 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 |
International Table calorie = cal(IT) thermochemical calorie = cal(th) mean calorie = cal(mean) 15 degree C calorie = cal(15C) 20 degree C calorie = cal(20C). |
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 1.355 818 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 # |
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 |
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 |
Btu/hour x 0.293 071 Btu/minute x 17.584 267 Btu/second x 1055.056 calories/hour x 0.001 163 # 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 # |
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 107 252 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 # |
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 # |
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 |
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 |
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 # |
Conversion Tables of Units for Science and Engineering The Dent Dictionary of Measurement The Economist Desk Companion The Encyclopaedia Britannica World Weights and Measures | 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. 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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