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 that derived from the United Kingdom), to the metric or SI (Système International) system.
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All countries in the world use the metric or S.I. systems to a greater or lesser extent, and most have abolished the use of non-metric units for almost all purposes; notable exceptions are the time units from minute to year, and the various non-S.I. 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. S.I. units have a lot of use in many scientific and engineering areas. The dual use of a different system other then metric or S.I. based in many small areas is common. For example, in the UK speed limit signs are often in mph, and in many niche areas a non-metric or S.I. unit remain in use.
The units of time have largely escaped the metrication debate, as they have been common to both metric and non-metric systems since the failure of metric hours to gain popular acceptance during the French Revolution. The metric system has the second as its base unit of time. 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 decimal multiples of the second. So for example, kilometres per hour is an accepted unit of speed in the metric system, but metres per second would be preferred in a scientific setting.
As stated, non-metric measures in air and sea transport retain worldwide dominance. The knot remains the prime unit of velocity for maritime and air navigation, and for aircraft flying, altitudes are universally calculated in feet 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.
With the ever-increasing importance of global trade, increasing harmonization of units of measurement and standards has taken place. 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 nonmetric units. Businesses which convert to metric standards frequently cannot compete with those which do not, due to the 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.
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.
Often, metrication involves not only changing the units with which quantities are measured, but also redesigning standards to use 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 25.40 mm is not a rational size, and thus the metric size of 25 mm is substituted. This requires the redesign not only of the bolt, but also of many other products and structures that would contain the bolt. It is often claimed that the changeover to common metric sizes by businesses and manufacturers is used as a opportunity to raise the price for a given amount of product, taking advantage of consumers' unfamiliarity with a new size.
The main exception to standardized metrication is the United States. Although metrication is the official policy of the U.S. government, 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 and engineering. However, change has occurred, with most products within the U.S. now labeled with both metric and nonmetric 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- and 12-ounce aluminum cans and 20-ounce PET bottles.
The U.S. (along with other countries) 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. Metric units are generally used in military and scientific applications in the USA with some exceptions like BTUs.
Europe generally uses metric units for almost all purposes, and uses metric standards. Some nonmetric units are still popularly used in some countries, including the pint and mile in the UK.
Metrication was first begun in France during the French Revolution, although many 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, with some limited exceptions.
The United Kingdom and Ireland are the main exceptions; these countries are in the process of phasing out the legal status of most nonmetric units. Thus they use a mixture of metric and nonmetric units for different purposes. The United Kingdom is currently in the process of abolishing the use of most nonmetric units; as of 2000, all loose goods sold by reference to units of quantity must be sold using metric units. UK policy is to eliminate almost all nonmetric units by 2009, except for road signs. The only non-metric units allowed after 2000 are:
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 (rarely encountered), 1/2 pint, or multiples of 1/2 pint.
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. However, it is required by law that all speed limit signs must be metric before December 31, 2004.
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 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 12.7mm (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 nonmetric 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 wallboard on old 16" spaced studs can be significantly difficult).
Also, many Canadians still use nonmetric units for common informal measurements. A person's height and weight are normally calculated using the US units foot and pound 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 which 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.
Fastfood restaurants often advertise measurements of food and drink in imperial units, either because the containers are made to American standards, or the franchise is American 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 and New Zealand have largely been converted to the metric system since the 1970s, but nonmetric units are still sometimes used in popular conversation, especially to measure body height or mass. (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, nonmetric 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.
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. Defenders of anti-metrication have become known colloquially in the UK as metric martyrs by other opponents of metrication. Such efforts to prevent metrication have largely failed, except in the United States.
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. 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. 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.
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. On the other hand only very few parts of the English systems use factor twelve, namely inch to foot and troy ounce to pound; two is most common, especially in volume measures, but overall a broad variety of conversion factors is used.
| 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 |
| powers | ||||
| ² | 64 | 100 | 144 | 256 |
| ³ | 512 | 1000 | 1728 | 4096 |
Another reason for anti-metrication is the difficulties that conversion to and from old units causes, although for everyday usage a 500-g pound, 4-l gallon and 25-mm inch would suffice. Moreover, 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, although the US one is based upon the English system, which in turn has largely Roman and French (e.g. Avoirdupois) roots.
In the United Kingdom, the anti-metrication cause is also linked with distrust of the European Union, 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.