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Metrication, or metrification, is the process of converting from the various other systems of units used throughout the world (especially the "Imperial" or "American" systems, originating in the United Kingdom) to the metric or SI (Système International) system.




All countries in the world use the metric or SI systems to a greater or lesser extent, and most have abolished the use of non-metric units for almost all purposes; a notable exception is the various non-SI units related to sea and air transport (as specified below).

The United States, Liberia, and Myanmar have not "officially" adopted everyday use of the metric system. Despite the lack of "official" adoption of the metric system in Liberia and Myanmar, unofficial metrication has taken place there, and the economies of these two countries do primarily operate using the metric system. Additionally, the United States Military makes extensive use of the metric system in its operations. SI units are commonly used in many scientific and engineering areas. The dual use of systems other than SI is common in certain areas. In the UK, for example, speed limit signs are still posted in miles per hour and other transitional or colloquial circumstances exist throughout the world.

SI is based on the MKS (Metre-Kilogram-Second) division of metric measurements. For a while there was heated contention with the CGS (Centimetre-Gram-Second) and some areas of science still use this form of the system, even though it is not the international standard any more. No meter-gram-second configuration was ever used which eliminated the prefixes entirely. There are a great number of derived units in both systems, and there is difficulty moving between branches of the Metric System on some of these units.


The base unit of time in the modernized metric system is the second. The minute, hour and day are officially "non-SI units accepted for use with the International System", even though for strict scientific use the SI recommends only the second and metric multiples and submultiples of the second. So for example, kilometres per hour (km/h) is an accepted unit of speed in the metric system, but metres per second (m/s) would be preferred in a scientific setting.

The original metric system did not include a metric time unit. Although decimal time was introduced in France after the French Revolution as part of the French Republican Calendar, it was not related to the metric system and was abandoned after two years for lack of public support, at the same time the metric system was introduced. Carl Friedrich Gauss advocated the addition of the second, defined as 1/86400 of a mean solar day, as a metric unit in 1832, which was later incorporated as a fundamental unit of both the CGS and MKS metric systems. The SI second has been redefined in terms of the vibrations of atoms for greater precision, since the exact length of the day varies slightly with the the rotation of the earth. Civil time in most countries is standard time, defined by offsets from Coordinated Universal Time, which is a time scale that is based upon a count of an integral number of SI seconds.

Air and sea transport

As stated, non-metric measures in air and sea transport retain worldwide dominance. In these areas the nautical mile (1.852 km) is preferred over the kilometre, because it closely represents a minute of arc of the circumference of Earth. While the metre was also based on the Earth with 100 km equal to an arc of 1 gon, those units of angle have not seen widespread use, though they do appear on some maps. The gon is a recent name for what is still also called a grad or grade; thus kilometre : centigrade : : nautical mile : minute of arc.

The knot, which is nautical miles per hour, remains the prime unit of speed for maritime and air navigation (although before the 1960s, statute miles per hour—which bear no relationship to the Earth—were most often used for this purpose, and they remained in fairly common use for some purposes into the 1970s and later). For aircraft flying, altitudes are in most places calculated from air pressure to feet (in steps of 100) rather than metres. Since aircraft pilots and air traffic controllers have long been trained to use non-metric units, the potential threat to air traffic safety has been cited as a reason for not adopting metric measurement in this area. Helicopter pilots and many Eastern European air forces (mainly, but not only former Warsaw Pact) are using metres, however.

Process of conversion

There are three possible major steps in converting from traditional measurements to metric:

  1. Allow the use of metric units,
    1. parallel with traditional ones,
    2. solely,
  2. base the definitions of traditional units upon their metric counterparts,
    1. make these redefinitions round metric values,
    2. decimalize the factors between traditional units,
  3. enforce metric units and disallow traditional ones.

Not all of these steps are necessary or advisable, but most have been taken by all countries over the past two centuries. For example, many local pounds have had been redefined to be 500 g exactly and are informally used to present day—the English ones (Avoirdupois and Troy) have not. The mere decimalization of old units, e.g. 10 inches to the foot (Sweden etc.), has been unsuccessful in most cases: people just fully converted to metric instead.


Metrication generally requires legislative action to overcome resistance and inertia among populations familiar with another system, i.e. legal requirements to use metric units in commerce, and the eventual prohibition of the use of non-metric units. Without such legislation businesses may not want to convert to metric standards, because of the habitual preference of consumers for the familiar. Those countries that have attempted to engineer a voluntary conversion to the metric system, such as the United States, have been largely unsuccessful. Countries that forced the change by making the metric system legally compulsory have been more successful.


With the ever-increasing importance of global trade, increasing harmonization of units of measurement and standards has taken place. This does not necessarily have to mean metrication: many Canadian and Mexican companies cannot fully metricate or even have to step back to using Imperial units because of the importance of the US market to their export trade.

Nice numbers

Often, but not necessarily, metrication involves redesigning standards to use smooth metric sizes. For example, 1 inch is a rational size for a bolt if the bolt is to be measured in inches, but the metric equivalent of 25.4 mm is not only not a rational size but does not even exist, and thus the metric size of M24 might be substituted. This requires not only selecting a different type of the bolt, but also a redesign of many other products and structures that would contain the bolt. In many other cases there is little difficulty, though.

Price adjustment

It is often claimed that the changeover to common metric sizes by businesses and manufacturers is used as an opportunity to raise the price for a given amount of product, taking advantage of consumers' unfamiliarity with a new size, but there have been a number of examples of the contrary (e.g. 2-litre Coca-Cola bottle). A common reason for continuing to display unit prices "per pound" as opposed to "per kilogram" is that the price appears half as much.

Insufficient communication

A single failure to convert between units was the contributing factor in the loss of the Mars Climate Orbiter in its crash on Mars. The manufacturer of the spacecraft had designed the navigation system to be programmed in Imperial measurements, whereas the navigation team at NASA's Jet Propulsion Laboratory in Pasadena, California controlled the spacecraft using metric units.

Metrication around the world

United States

See also: Metric system in the United States

The main exception to standardized metrication is the United States. Although metrication is the official policy of the U.S. government since the Metre Convention, the progress of metrication has been much slower in the U.S. than in the rest of the world. Non-metric units continue to be almost exclusively used in everyday life, and in commerce, engineering, and aviation. However, change has occurred, with most products within the U.S. now labeled with both metric and non-metric units, and a number of companies and government agencies switching to metric standards.

One peculiar example of this is bottled soft drinks, commonly sold in units of two liters with units of one and three being less common. This is a result of the introduction of PET bottling technology coinciding with a particularly strong metrication push in the late 1970s; consumers found that they could buy a two-liter plastic bottle of their favorite soft drink more cheaply than they could four one-pint glass bottles, and the convention stuck. Smaller units, however, continue to be sold in fluid ounces, as with 8-ounce (240 ml) and 12-ounce (355 ml) aluminum cans and 20-ounce (591 ml or 600 ml) PET bottles.

The U.S. continues to use only miles for road distance signs, with the exception of Interstate 19 in Arizona. Originally U.S. legislation set October 2000 as a deadline by which states must undertake construction work and statistics in metric for states to be eligible for federal funding, but that requirement has since been rescinded. Some states, such as California, have experimented with metric road signs, but there are as yet no plans for large-scale conversion. At least there are federally standardized metric and dual-unit road signs, that could be used—not following any international standard for road signs, though.

Metric units are generally used in military and scientific applications in the USA with some exceptions like BTUs.

Metrication of property title in the United States is not likely in the foreseeable future. Land titles in most of the country are tied to the Public Land Survey System, which was largely completed before the mile was redefined in terms of the metric system. In the creation and definition of survey townships, PLSS uses statute miles, which differ from metric-referenced miles by a few millimeters.


Europe generally uses metric units for almost all purposes, and uses metric standards. Some non-metric units are still popularly used in some countries, including the pint and mile in the UK. In other cases, the term for a traditional measure has been affixed to a metric one. For instance, the Continental "metric pound" (German Pfund, French livre, or Dutch pond) is popularly defined as 500 grams.

Metrication was first begun in France during the French Revolution, although some of these revolutionary efforts were abandoned. The metrication of units of time was originally a part of the plan, but this failed to receive popular support. By about 1900, metrication had spread over much of continental Europe.

Metrication for all European Union member states is required under EU law, with a target date of 2009 by which all products in Europe must be sold only by metric units.

UK and Ireland

The United Kingdom and the Republic of Ireland are the main exceptions; these countries are in the process of phasing out the legal status of most non-metric units. Thus they use a mix of metric and non-metric units for different purposes. The United Kingdom is currently in the process of abolishing the use of most non-metric units; as of 2000, all loose goods sold by reference to units of quantity had to be sold using metric units. UK policy is to eliminate almost all non-metric units by 2009 except for road signs. The only non-metric units allowed after 2000 are:

  • The mile, yard, foot and inch for road signs and related uses,
  • the acre for land registration,
  • the troy ounce for trading in precious metals,
  • the foot for aircraft altitudes,
  • the nautical mile and knots for sea and air traffic,
  • the pint for draught beer and cider and for milk when sold in returnable containers.

Draught beer and cider are the only goods that may not be sold in metric units in the United Kingdom; the only legal measures for these drinks when sold on draught are 1/3 pint (190 ml) (rarely encountered), ½ pint (284 ml) and integer multiples of the latter.

Ireland generally uses metric measurements more than the United Kingdom, but still less than the rest of Europe. Confusingly, road distance signs were progressively converted to kilometres during the 1990s, but speed limit signs (and the associated road traffic legislation) are still in mph. The government of the Republic of Ireland has set 20 January 2005 as the official date by which road speed limits must be converted. New vehicles with metric-only instruments can only be sold after 1 January 2005. Some manufacturers of automobiles began selling metric-only vehicles in the autumn of 2004. This will be a major change as it will affect the used car market between the UK and Ireland. Irish road distance signs must be converted to metric before the end of 2005.

The use of metric units has been legal in the UK for all purposes since 1897. Despite the slow progress of metrication, its sole adoption was first recommended by the Committee on Weights and Measures (Hodgson Committee) in 1950, and accepted by the President of the Board of Trade in May 1965. As a result, metric units have been taught in UK schools since the late 1960s, and certain industries also converted or largely converted decades ago. For example the paper industry converted in 1970, and the construction industry between 1969 and 1972—although certain products continue to be produced to imperial sizes but with metric size descriptions, for example as 13 mm (rather than as half-inch) thick plasterboard.


Canada has converted to the metric system for most purposes, including temperature in weather reports, speed limits, road signs, and sizes of most products. However there is still significant use of non-metric units and standards in some sectors of the Canadian economy, mainly due to the close proximity to the United States. Notable among these are stationery, construction lumber, and drywall—retrofitting metric-sized (designed for 400 mm centres) wallboard on old 16" (406.4 mm) spaced studs can be significantly difficult.

Also, many Canadians still use non-metric units for common informal measurements. A person's height and weight are normally calculated using the U.S. units foot and pound (except in highly urbanized centres) while area (for reasonably small areas such as floorspace) is measured in square feet. Fahrenheit is used for cooking as are US cooking measurements.

Grocery stores advertise most products sold by weight in both price per pound and per kilogram but the pound price is prominent mainly because the price per pound appears cheaper than the price per kilogram. The biggest exception is deli items that are sold (and advertised) per 100 g. Since the price per 100 g appears cheaper than the price per pound, it is usually the only price listed. Most Canadians order their deli items in metric quantities.

Fast-food restaurants often advertise measurements of food and drink in imperial units, either because the containers are made to U.S. standards, or the franchise is U.S. based and uses a standard size for its products, or to make it more difficult for consumers to compare prices between the restaurant's products and those of grocery stores.

Australia, New Zealand and South Africa

Australia and New Zealand have largely been converted to the metric system since the 1970s, but non-metric units are still sometimes used in popular conversation, especially to measure body height—many Australians know their height in feet and inches but their mass in kilograms. In South Africa, where the conversion to metric was completed in 1978, non-metric measurements are rarely encountered in popular conversation, and use of the decimal comma (used in European languages) is often encountered in South African English, instead of the decimal point, as is the case elsewhere in the English-speaking world.


In Australia, a metrication board was created in 1966 and dissolved in 1981 once the conversion to metric was completed. During this time, a Metric Conversion Act was passed. For additional background, see the report Metrication in Australia by Kevin Joseph Wilks (DITAC - Department of Industry, Technology and Commerce).

The anti-metrication movement

Anti-metrication (or anti-metrification) is rejection of metrication in favor of a different system of measurement, typically the American or the different UK Imperial one. Such efforts to prevent metrication have largely failed, except in the United States.

Some opponents of metrication have become known colloquially in the UK as metric martyrs (the term is used by both supporters and opponents of metrication).

Human scale

The basic philosophy of anti-metrication is that non-metric systems of measurement were developed organically from actual use (thus units which share names with physical objects, such as the foot, hand, barrel, cord) and are therefore properly suited for normal usage, whereas the metric system is based on easy decimal conversion between various units, not natural usage.


Divisor Imperial (base 8) Metric (base 10) Imperial (base 12) Imperial (base 16)
2 4 5 6 8
3 2.667 3.333 4 5.333
4 2 2.5 3 4
5 1.667 2 2.4 3.333
6 1.333 1.667 2 2.667
7 1.143 1.429 1.714 2.286
8 1 1.25 1.5 2
9 0.889 1.111 1.333 1.778
10 0.8 1 1.2 1.6
² 64 100 144 256
³ 512 1000 1728 4096

Apart from the natural sizes of evolved units, another reason for preferring non-metric units is the ease with which they can be divided by common fractions, for example, dividing by three is simple in a base 12 system, but difficult in a base ten. Even taking a quarter in base ten gives a fraction, whereas in many non-metric systems this too is easy. Actually very few parts of the English systems use factor twelve, namely inch to foot and troy ounce to pound. Binary (factor two) is more common, especially in volume measures, but other conversion factors (5, 7, 11) are used.

Conversely, SI contains no specified preferred sizes, despite the existence of Reynard series and others. As an example, construction components are based on the 100 mm or decimetre module and it is common to find products in sizes of 1200 mm × 2400 mm, 2400 mm × 4800 mm, etc. Stud spacings are usually 400 mm or 600 mm. All sizes chosen are a multiple of the 100 mm module. Sizes are often based around powers of 2 or 12 to take advantage of the familiarity or connivance in other systems.

Another reason for anti-metrication is the difficulties that conversion to and from old units causes. For everyday usage a 500-g pound, 4-l gallon and 25-mm inch could suffice, and have been used.


For some, anti-metrication is a form of traditionalism, looking to a history of usage that stretches back centuries or even millennia. Sometimes it is even considered part of patriotism. For traditional argument, however, the US system is based upon the English system, which in turn has largely Roman and French (i.e. Avoirdupois) roots.

The non-metric units have changed meanings many times throughout history. At the time of the French revolution there were over 5000 variations on the foot alone. Which one would be traditionally correct? The so-called Imperial system is the result of a clean-up in 1824, some 30 years after the founding of the metric system. Even in those days there was resistance to Imperial from users of the abolished older units.

Metric units, however, have not been exempt of redefinitions or refinements. The metre for instance was intended to equal 10−7 or one ten-millionth of the length of the meridian through Paris from pole to the equator. However, the first prototype was short by 0.2 millimeters because researchers miscalculated the flattening of Earth due to its rotation. Now it is the length travelled by light in vacuum during the time interval of 1/299 792 458 of a second.


Another complaint regarding SI is the alleged unpleasantness of its terms. Supporters of other systems claim that, being designed for scientific use, most metric terms are "cold", "harsh" and lack the character of their Imperial counterparts.

For example, most common Imperial measurement, save "gallon", are single-syllable (inch, foot, yard, mile, ounce, pound, ton, cup, pint, quart) which would be more "appealing" to the tongue and ear than "lifeless" terms like decimetre or millilitre; in English, the names of the metric units, with their prefixes of multiple origins are imperfectly domesticated loanwords. The corresponding traditional units, though not all of Anglo-Saxon etymology, have been in use long enough to thoroughly conform to regular English phonology. The irregular correspondence between spelling and pronunciation of a foreign word like liter, by contrast, marks it as an intruder.

While there are those who claim this objection is mere parochialism , its existence can be helpful in understanding how much people "hold dear" the units they grew up with, and the difficulties encountered in the metrication process.

Government compulsion

Another basic argument is that the adoption of metric units has almost always been a matter of government compulsion, prohibiting people from using units they were used to, and that such policies are wrong in principle. The idea of compulsory standards is hardly new: in the 1820s, Great Britain consolidated the various "gallons" in use at the time and established a new imperial gallon, simultaneously prohibiting the use of the older units.

Anti-metrication in the UK often manifests itself in conjunction with Euroscepticism because of the belief that the European Union is responsible for compulsory metrication, although metrication had been government policy since 1953 and the process was initiated by the government establishing the Metrication Board in 1969, four years before joining the EC. In more recent times, anti-metrication supporters have claimed that the legal compulsion to adopt the metric system instead of their traditional weights and measures is an infringement of their human rights to freedom of speech, though this claim has been consistently rejected by the courts. Most recently, on 25 February 2004, the European Court of Human Rights rejected an application from British shopkeepers refusing to use metric claiming that their human rights had been violated.

Ideology of the metric system

The metric system was invented by French scientists, and was proposed for widespread non-scientific use as a result of the French Revolution of 1789. The metric system was designed as part and parcel of the revolution's official ideology of "Pure Reason".

As a part of the original package of imposing "Pure Reason" on weights and measures, the original package included the French revolutionary calendar; this calendar was designed as an explicit attack on the Christian year, replacing the week with decades of ten days, thereby removing the sabbath or the Lord's Day as a regular part of the calendar. In addition to the new calendar, the original package also included metric time, dividing the day into 10 "hours" with 100 "minutes".

Napoleon Bonaparte abolished the metric calendar to meet the objections of the Roman Catholic Church in 1806. Decimal time died of neglect well before that, while other measurements (gram, litre, metre) persisted. It has been argued that the metric system suffers from monomaniacal decimalism, i.e. a "tunnel visioned" insistence on ten as the sole multiplier or divisor among permitted units, and thereby sacrifices convenience and human scale for the sake of mathematics. This intrudes "Pure Reason" where opponents say it does not belong.

Related international standards

Although the metric system is for specifying products and their components only, lumped in with the notion of metrication is often the acceptance of a whole set of international standards:

  • Sizes of standard paper, the reams in which they are packed, the locations of holes for ring binders, and the boxes and filing cabinets which contain them;
  • though the geographic measurements on maps are of course in meters and kilometres, the scales of the maps themselves are limited to a few standard ones;
  • bed frames, mattresses, and their sheets;
  • not only the trivial grocery changes of butcher's meat scales and the change of liquor from a fifth of a gallon to 750 millilitres (which sometimes resulted in similar changes in the metric world, such as a change of German wine bottles from 700 mL to 750 mL), but also the entire range of cans for preserving foods.

These are what international organizations have specified and have been taken up in fully metric countries. Only the sizes of shoes and clothing are usually multiply labelled.

See also

External links


  • [1] - discusses progress of metrication in several countries, from the U.S. Metric Association


  • [2] - the United Kingdom Metric Association campaigns for a total metric switchover in the UK.


  • [3] - discusses the freedom to choose a measurement system
  • [4] - Metrication as a destruction of culture
Last updated: 02-26-2005 13:09:46