Cleave Books
A Dictionary of Units ~ Part 2
by Frank Tapson

This provides a summary of most of the units of measurement to be found in use around the world today (and a few of historical interest), and the definitions and rules of the various systems in which they are found.

Conversions between the various units are dealt with in Part 1

  There are NO units of currency.  
  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.  
And then there is its   publishing history .  

There is a separate document covering the most   FAQ and other measures.  

The Systeme International [S I]

Le Systeme international d'Unites officially came into being in October 1960 and has been officially recognised and adopted by nearly all countries, though the amount of actual usage varies considerably. It is based upon 7 principal units, 1 in each of 7 different categories -

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
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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Definitions of the Seven Basic S I Units

metre [m]
The metre is the basic unit of length. It is the distance light travels, in a vacuum, in 1/299792458th of a second.
kilogram [kg]
The kilogram is the basic unit of mass. It is the mass of an international prototype in the form of a platinum-iridium cylinder kept at Sevres in France. It is now the only basic unit still defined in terms of a material object, and also the only one with a prefix[kilo] already in place.
second [s]
The second is the basic unit of time. It is the length of time taken for 9192631770 periods of vibration of the caesium-133 atom to occur.
ampere [A]
The ampere is the basic unit of electric current. It is that current which produces a specified force between two parallel wires which are 1 metre apart in a vacuum.It is named after the French physicist Andre Ampere (1775-1836).
kelvin [K]
The kelvin is the basic unit of temperature. It is 1/273.16th of the thermodynamic temperature of the triple point of water. It is named after the Scottish mathematician and physicist William Thomson 1st Lord Kelvin (1824-1907).
mole [mol]
The mole is the basic unit of substance. It is the amount of substance that contains as many elementary units as there are atoms in 0.012 kg of carbon-12.
candela [cd]
The candela is the basic unit of luminous intensity. It is the intensity of a source of light of a specified frequency, which gives a specified amount of power in a given direction.
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Derived Units of the S I

From the 7 basic units of the SI other units are derived for a variety of purposes. Only a few of are explained here as examples, there are many more.
farad [F]
The farad is the SI unit of the capacitance of an electrical system, that is, its capacity to store electricity. It is a rather large unit as defined and is more often used as a microfarad. It is named after the English chemist and physicist Michael Faraday (1791-1867).
hertz [Hz]
The hertz is the SI unit of the frequency of a periodic phenomenon. One hertz indicates that 1 cycle of the phenomenon occurs every second. For most work much higher frequencies are needed such as the kilohertz [kHz] and megahertz [MHz]. It is named after the German physicist Heinrich Rudolph Hertz (1857-94).
joule [J]
The joule is the SI unit of work or energy. One joule is the amount of work done when an applied force of 1 newton moves through a distance of 1 metre in the direction of the force.It is named after the English physicist James Prescott Joule (1818-89).
newton [N]
The newton is the SI unit of force. One newton is the force required to give a mass of 1 kilogram an acceleration of 1 metre per second per second. It is named after the English mathematician and physicist Sir Isaac Newton (1642-1727).
ohm [Ω]
The ohm is the SI unit of resistance of an electrical conductor. Its symbol, is the capital Greek letter 'omega'. It is named after the German physicist Georg Simon Ohm (1789-1854).
pascal [Pa]
The pascal is the SI unit of pressure. One pascal is the pressure generated by a force of 1 newton acting on an area of 1 square metre. It is a rather small unit as defined and is more often used as a kilopascal [kPa]. It is named after the French mathematician, physicist and philosopher Blaise Pascal (1623-62).
volt [V]
The volt is the SI unit of electric potential. One volt is the difference of potential between two points of an electical conductor when a current of 1 ampere flowing between those points dissipates a power of 1 watt. It is named after the Italian physicist Count Alessandro Giuseppe Anastasio Volta (1745-1827).
watt [W]
The watt is used to measure power or the rate of doing work. One watt is a power of 1 joule per second. It is named after the Scottish engineer James Watt (1736-1819).
Note that
prefixes may be used in conjunction with any of the above units.
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The Prefixes of the S I

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
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)
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
[µ] the symbol used for micro is the Greek letter known as 'mu'
Nearly all of the S I prefixes are multiples (kilo to yotta) or sub-multiples (milli to yocto) 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!
Call up a Conversion Calculator for Prefixes
OR Notes on Prefixes (inc. other types)
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Conventions of Usage in the S I

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.
  • Any unit may take only ONE prefix. For example 'millimillimetre' is incorrect and should be written as 'micrometre'.
  • Most prefixes which make a unit bigger are written in capital letters (M G T etc.), but when they make a unit smaller then lower case (m n p etc.) is used. Exceptions to this are the kilo [k] to avoid any possible confusion with kelvin [K]; hecto [h]; and deca [da] or [dk]
  • It will be noted that many units are eponymous, that is they are named after persons. This is always someone who was prominent in the early work done within the field in which the unit is used. Such a unit is written all in lower case (newton, volt, pascal etc.) when named in full, but starting with a capital letter (N V Pa etc.) when abbreviated. An exception to this rule is the litre which, if written as a lower case 'l' could be mistaken for a '1' (one) and so a capital 'L' is allowed as an alternative. It is intended that a single letter will be decided upon some time in the future when it becomes clear which letter is being favoured most in use.
  • Units written in abbreviated form are NEVER pluralised. So 'm' could always be either 'metre' or 'metres'. 'ms' would represent 'millisecond'.
  • An abbreviation (such as J N g Pa etc.) is NEVER followed by a full-stop unless it is the end of a sentence.
  • To make numbers easier to read they may be divided into groups of 3 separated by spaces (or half-spaces) but NOT commas.
  • The SI preferred way of showing a decimal fraction is to use a comma (123,456) to separate the whole number from its fractional part. The practice of using a point, as is common in English-speaking countries, is acceptable providing only that the point is placed ON the line of the bottom edge of the numbers (123.456) and NOT in the middle.
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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.

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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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

				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 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
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.
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Metrication in the U K

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 -

  • pounds and ounces for weighing of goods sold from bulk
  • pints and fluid ounces for beer, cider, waters, lemonades and fruit juices in RETURNABLE containers
  • therms for gas supply
  • fathoms for marine navigation
could be used until 31st December 1999.

The following could continue to be used WITHOUT time limit -

  • miles, yards, feet and inches for road traffic signs and related measurements of speed and distance
  • pints for dispensing draught beer and cider, and for milk in RETURNABLE containers
  • acres for land registration purposes
  • troy ounces for transactions in precious metals.
Sports were exempt from all of this, but most of them have (voluntarily) changed their relevant regulations into statements of equivalent metric measures.

That was how the legislation was framed. In common usage the 'old' units are still very apparent.

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 yard 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 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

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!

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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

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)

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 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
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.
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Other Sources in Books

Conversion Tables of Units for Science and Engineering
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.

The Dent Dictionary of Measurement
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.

The Economist Desk Companion
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 Encyclopaedia Britannica
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.

World Weights and Measures
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.

British Weights and Measures
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.

The World of Measurements
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.

Scientific Unit Conversion
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

There are now several sites concerned with this topic. (It is popular with those wishing to start up a site.) Almost all the Search Engines will find links to more sites than anyone could really need, and each of those will give more links . . . . .
The problem is simply: which one best suits the purpose?

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 UK Metric Association. 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, practical usage and many other points of interest, all get a mention.

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.

The US Metric Association is also a good starting point which provides a wealth of links to other suitable sites.

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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And here is a very brief biographical note about the author.

Go to Cleave Books Home Page.
Publishing history
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)
1st May 2001 (Link to 'FAQ and other measures' put in)
2nd December 2001 (Several minor alterations throughout and 2 corrections made)
18th March 2002 (More links added)
1st August 2002 (Major makeover, and the 40th Conversion Calculator added)
1st December 2003 Dictionary divided into two parts.
©Frank Tapson 2004