Metrication (or metrification) refers to the introduction of the SI metric system as the international standard for physical measurements—a long-term series of independent and systematic conversions from the various separate local systems of weights and measures. Metrication began in France in the 1790s and spread widely during the following two centuries.

All countries across the globe have officially adopted the metric system except the United States of America, Liberia and Burma (Myanmar). These remaining countries have not officially adopted metric but have done so to some degree indirectly through international trade and standardisation. Liberia and Myanmar are both substantially metric countries that trade internationally in metric units. Visitors to these places report that they also use metric units for most things internally with only a few exceptions like old (ancient) petrol pumps calibrated in British Imperial gallons. Most countries have adopted the metric system officially over a transitional period where both units are used for a set period of time. Some countries such as Guyana, for example, have officially adopted the metric system, but have had some trouble over time implementing it. Antigua, also 'officially' metric, is moving toward total implementation of the metric system, but slower than expected. Other Caribbean countries such as Saint Lucia are officially metric but are still in the process toward full conversion.

In the European Union, with the Units of Measure Directive, the European Council (of Ministers) sought to achieve a common system of weights and measures to further the aims of the European Single Market. A part of the negotiations towards the Directive, the United Kingdom secured permanent exemptions for the mile and yard in road markings, and (with Ireland) for the pint for beer and milk. Throughout the 1990s, the European Commission helped accelerate the process for member countries to complete their conversion process to metric. In 2007, the European Commission also announced that (to facilitate trade with the United States) it was to abandon the requirement for metric-only labelling on packaged goods, and to allow dual metric-imperial marking to continue indefinitely.

Other countries in the former British Empire completed metrication during the second half of the 20th century, the most recent being the Republic of Ireland, which finalised conversion in early 2005 after beginning in the 1970s.

The United States and the United Kingdom see active opposition to metrication today for a number of reasons. Other countries, like France and Japan, once had significant popular opposition for similar reasons, but today enjoy complete acceptance of metrication.

Before the metric system

In medieval Europe, local laws on weights and measures were set by trade guilds on a city-by-city basis. For example, the ell or elle was a unit of length commonly used in Europe, but its value varied from 40.2 centimetres in one part of Germany to 70 centimetres in The Netherlands to 94.5 centimetres in Edinburgh. A survey of Switzerland in 1838 revealed that the foot had 37 different regional variations, the ell had 68, there were 83 different measures for dry grain and 70 for fluids, and 63 different measures for "dead weights". When Isaac Newton wrote Philosophiae Naturalis Principia Mathematica in 1687, he quoted his measurements in Parisian feet so readers could understand the size. Examples of efforts to have local intercity or national standards for measurements include the Scottish law of 1641, and the British standard Imperial unit system of 1845, which is still commonly used in the UK. At one time Imperial China had successfully standardised units for volume throughout its territory, but by 1936 official investigations uncovered 53 dimensions for the chi varying from 200 millimetres to 1250 millimetres; 32 dimensions of the cheng, between 500 millilitres and 8 litres; and 36 different tsin ranging from 300 grams to 2500 grams. However, revolutionary France was to produce the definitive International System of Units which has come to be used by most of the world today.

The desire for a single international system of measurement derives from growing international trade and the need to apply common standards to goods. For a company to buy a product produced in another country, they need ensure that the product will arrive as described. The medieval ell was abandoned in part because its value could not be standardised. It can be argued that the primary advantage of the International System of Units is simply that it is international, and the pressure on countries to conform to it grew as it became increasingly an international standard. SI is not the only example of international standardisation; several powerful international standardisation organisations exist for various industries, such as the International Organisation for Standardisation, the International Electrotechnical Commission, and the International Telecommunication Union.

Conversion process

There are three common routes that nations take in converting from traditional measurement systems to the metric system. The first is a quick, so called "Big-Bang" route which was successfully used by Australia and India in the 1960s and several other developing nations since then. The second route is to phase-in units over time, and progressively outlaw traditional units. This method, favoured by industrial nations, is slower and generally less successful. The final route is to redefine traditional units in metric terms. This method has been used successfully where traditional units were ill-defined and had regional variations.

The first route, "Big-Bang", is to simultaneously outlaw the use of pre-metric measurement, metricise, reissue all government publications and laws, and change education systems to metric. India's changeover lasted from 1 April 1960, when metric measurements became legal, to 1 April 1962, when all other systems were banned. The Indian model was extremely successful and was copied over much of the developing world.

The second possibility, and first phase-in route, is to pass a law permitting the use of metric units in parallel with traditional ones, followed by education of metric units, then progressively banning the use of the older measures. This has generally been a slow route to metric. The British Empire permitted the use of metric measures in 1873, but the changeover was not completed in most countries until the 1970s and 1980s when governments took an active role in the now-independent parts of the empire. Japan, too, followed this route and did not complete the changeover for 70 years. In the United Kingdom, the process is still incomplete. By law, loose goods sold with reference to units of quantity have to be weighed and sold using the metric system. Until September 11 2007 British law stated that non-metric labeling on packages would become illegal after December 2009, however the European Union has since granted the UK the right to use supplementary measures (imperial units alongside metric) indefinitely. (See metrication in UK for details.)

A final possibility is to redefine traditional units in terms of metric values. These redefined "quasi-metric" units often stay in use long after metrication is said to have been completed. China followed this route, and thus while scientists in China know and use the kilogram, common people retain the jin (catty), which now has a value of 500 g. In the Netherlands, 500 g is informally referred to as a pond (pound) and 100 g as an ons (ounce), and in Germany and France 500 g is informally referred to respectively as ein Pfund and une livre . In Denmark, the re-defined pund (500 g) is occasionally used, particularly among older people and (older) fruit growers, since these were originally paid according to the number of pounds of fruit produced. In Sweden and Norway a mil (mile) is informally equal to 10 km, and this has continued to be the predominantly used unit in conversation when referring to geographical distances. In the 19th century Switzerland had a non-metric system completely based on metric terms, e. g. 1 Fuss (foot) equal to 0.30 m = 10 Zoll (inches) equal to 0.03 m = 10 Linien (lines) equal to 0.003 m.

It is difficult to judge the degree to which ordinary people change to using metric in their daily lives. In countries that have recently changed, older segments of the population tend to still use an older and more familiar system. Also, local variations abound in what exactly becomes metricated and what does not. In Canada, for example, ovens and cooking temperatures are usually measured in degrees Fahrenheit, and Canadians almost invariably use Fahrenheit for cooking; though this is not necessarily by choice but may instead be due to the overwhelming influence of the neighbouring and largely non-metricated United States. In the UK, which is still in the process of changing over completely, Fahrenheit is seldom encountered (except when some people talk about hot summer weather) while other metric units are often used in conjunction with older measurements, and road signs use miles rather than kilometres. Such countries could be said to be "semi-metric".


As of 2007, the metric system dominates all but three countries — Burma, Liberia, and the United States — but traditional units are still used in many places and industries. For example, automobile tire pressure is measured as psi in countries such as Brazil and Argentina which are otherwise completely metric. Office space is often rented in traditional units, such as square foot in Hong Kong, tsubo in Japan or pyoung in Korea (use of these units is to be subject to a fine in South Korea beginning July 2007). Traditional measurements are still used in some areas, e.g. in plumbing the diameters of pipes are still measured in inches in some countries (in the UK all new pipes are metric). Automotive wheel diameters are still set as whole inch measurements (though tyre widths are measured in millimetres) and dots per inch continues to be used in describing graphical resolution in the computer industry. Television and monitor screen diameters are still commonly cited in inches in many countries; however in Australia and South Africa, centimetres are often used for televisions sets, whilst CRT computer monitors and all LCD monitors are measured in inches. The only exception to the metrication process in Ireland was the pint in bars, pubs and clubs; though alcohol sold in any other location is in metric units (usually 330 ml (canned beer), 500 ml (bottled beer), 750 ml (wine) or 1 l (spirit)). In Australia, a pint of beer was redefined to 570 ml (see Australian beer glasses). In both metric and non-metric countries, racing bicycle frames are generally measured in centimetres, while mountain bicycle frames are measured in inches.

In some countries (like Antigua, see above), the transition is still in progress. The Caribbean island nation of Saint Lucia announced metrication programs in 2005 to be compatible with CARICOM. In the United Kingdom, the metric system is compulsory in most, but not all, industries. In the UK, the metric system had been legal for nearly a century before metrication efforts began in earnest. The government had been making preparations for the conversion of the Imperial unit since the 1862 Select Committee on Weights and Measures recommended the conversion and the Weights and Measures Act of 1864 and the Weights and Measures (Metric System) Act of 1896 legalised the metric system. In 1965, with lobbying from British industries and the prospects of joining the European Community, the government set a 10 year target for full conversion and created the Metrication Board in 1969. Metrication did occur in many areas during this time period, including the re-surveying of Ordnance Survey maps in 1970, decimalisation of the currency in 1971, and teaching the metric system in schools. However, no date was set for making the use of the metric system compulsory, and the Metrication Board was abolished in 1980 following a change in government. The 1989 European Units of Measurement Directive (89/617/EEC) required all member states to make the metric compulsory; however, the British negotiated certain derogations (delayed switchovers), including miles for road signs, and pints for draught beer, cider, and milk sales. Advocacy groups such as the Metric Martyrs, the British Weights and Measures Association, and the Active Resistance to Metrication continue to resist the compulsory use of the metric system, on the grounds that some surveys have shown that a lot of British people do not think in metric terms and because physical repackaging into rounded metric numbers could lead to reducing the quantity of goods sold for the same price. It should, however, be noted that some items have been rounded up during metric changeover, for example spirits were changed from of a gill (23.7 ml) to 25 ml and the standard loaf from 14 ounces (396.9 g) to 400 g.

Non-metric countries

Liberia, Burma (Myanmar), and the United States are the three countries that have yet to adopt metric as their official system of measurement. However, as previously mentioned, these countries have been influenced by metric over time through international trade and standardization. The history of metric in the United States actually goes much deeper. In the United States the use of the metric system was made legal as a system of measurement in 1866 and the United States was a founding member of the International Bureau of Weights and Measures in 1875. The system was officially adopted by the federal government in 1975 for use in the military and government agencies. In 1985, the metric system was made the preferred (but predominantly voluntary) system of weights and measures for United States trade and commerce (see Metrication in the United States). It has remained voluntary for federal and state road signage to use metric units, despite attempts in the 1990s to make it a requirement. A 1992 amendment to the Fair Packaging and Labeling Act (FPLA), which took effect in 1994, required labels on federally regulated "consumer commodities to include both metric and U.S. customary units. An amendment that would allow (but not require) metric-only labels is currently under consideration, and all but two US states (New York and Alabama) have passed laws permitting metric-only labels for the products they regulate. Likewise, Canada also legally allows for dual labeling of goods provided that the metric unit is listed first and that there is a distinction of whether a liquid measure is a U.S. or a Canadian (Imperial) unit. Today, the American public and much of the private business and industry still use U.S. customary units despite many years of informal or optional metrication. At least two states, Kentucky and California, have even moved towards demetrication of highway construction projects.

Air and sea transport

Some industries have resisted metrication. Non-metric measures of speed in air and sea transport retain worldwide dominance. In these areas the nautical mile is used. The prime unit of speed for maritime and air navigation remains the knot (nautical mile per hour).

The prime unit of measure for aviation (altitude) is usually estimated based on air pressure values and described in nominal feet rather than nominal metres. A vertical spacing of 1,000 feet has become the standard measure for safety and clarity for purposes of air traffic control. However, several countries and air forces use metres for altitude today. The policies of the International Civil Aviation Organization (ICAO) relating to measurement are:

  • there should be a single system of units throughout the world
  • the single system should be SI
  • the use of the foot for altitude is a permitted variation

Consistent with ICAO policy, aviation has undergone a significant amount of metrication over the years - for example runways are usually given in metres. The United States metricated temperature reports in 1996. Metrication is also gradually taking place in cargo weights/dimensions and fuel volume/weight.

Accidents and incidents

Confusion over units during the process of metrication can sometimes lead to accidents. One of the most famous examples is the Gimli Glider, a Boeing 767 that ran out of fuel in Canada in 1983 due, in large part, to confusion at Air Canada during Canada's metrication.

While not strictly an example of national metrication, the use of two different systems was a contributing factor in the loss of the Mars Climate Orbiter in 1998. NASA specified metric units in the contract. NASA and other organisations worked in metric units but one subcontractor, Lockheed Martin, provided thruster performance data to the team in pound force seconds instead of newton seconds. The spacecraft was intended to orbit Mars at about altitude but the incorrect data meant that it descended to about and probably burned up in the Martian atmosphere.


Interestingly, considering it was the birthplace of the metric system, France experienced a particularly rough journey to metrication. The traditional French measuring system was chaotic, with size of units differing in each small town, and often even within towns. Lyon had two different values of pound in general use, one of 14 ounces, and another of 15 ounces, the latter only being used for measuring silk. The revolutionary government, which saw the newly conceived metric system (commissioned by the previous king) as a good fit for its ideology of "pure reason", first attempted a quick conversion, legalising metric units in 1795 and, just four years later, banning the use of traditional units. Massive popular opposition led Napoleon, after he came to power, to roll back these reforms. He publicly denounced the previous government for "tormenting people with trifles". It appears that it was decimalisation that disturbed the people most — as, although Napoleon decreed that there should be "such fractions and multiples as were generally used", he redefined the old base units in metric terms. The original metric system was made law again in France in 1837.

Japan also saw popular resistance to its 1920s metrication program, where opponents of the metric system believed that the adoption of a foreign measuring system would have a bad influence on national sentiment, cause dislocations in public life and needless expense to the nation, prove disadvantageous to foreign trade, and hurt the national language and culture. In 1933, the government postponed the date of the first stage of conversion by five years, and the date of the second stage by ten years. The U.S. occupation resulted in a temporary conversion to U.S. customary units. The post-war manufacturing boom required an international standard measurement system and the issue was pursued again in the 1950s and 1960s. The process was not completed until 1969. Traditional units are, however, still used for measurements of sake and the area of land and apartments. Nevertheless, local units had been defined in terms of metric units (e.g., 1 shaku = 10/33 metre) as early as 1891. For the measurement of sake, 10 Japanese cups (180 millilitres each) equal 1 shō (traditional flask size of 1.8 litre capacity). Rice cookers are typically sold as having capacities such as 5 cups or 10 cups. (Note that the traditional Japanese cup is 180 millilitres while the American cup is 237 millilitres. )

Overall, few countries have experienced much popular opposition to metrication. Some, such as 19th century European countries, Russia, India and China, converted before most of their populations were literate, so the initial conversion affected few people. For others, such as Ireland, the previous system (i.e., imperial) was seen as foreign.

In the United Kingdom, the issue remains controversial as it becomes bound up with issues of tradition and national symbolism.

See also


External links

Websites supporting metrication:

Books supporting metrication:

  • Metric Signs Ahead (UKMA) (2005) by Robin Paice (ISBN 0955235123)
  • A Very British Mess (UKMA) (2004) by Robin Paice (ISBN 0750310146)

Websites opposing metrication:

Books opposing metrication:

  • The General Rule by Vivian Linacre (ISBN 1906069018)
  • About the Size of It by Warwick Cairns (ISBN 0230016286)

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