U.S. customary units

The U.S. customary units, commonly known in the United States as English units or standard units, are the non-SI (non-metric) units of measurement that are currently used in the U.S., in some cases alongside the International System of Units. This system of units is similar to, but not to be confused with, the Imperial system still used in the United Kingdom. Both systems derive from the evolution of local units over the centuries as a result of standardization efforts in England; the local units themselves mostly trace back to Roman and Anglo-Saxon units. Today, U.S. customary units are defined in terms of SI units.

Related Topics:
United States - English units - SI - Unit - International System of Units - Imperial system - United Kingdom - England

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The official policy of the United States government is to designate the metric system of measurement as the preferred system of weights and measures for U.S. trade and commerce. This process is known as metrication, and is evident in labeling requirements on food products, for example. However, for various reasons, customary units are still widely used on consumer products and in industrial manufacturing; only in specific scientific contexts are SI units always preferred. Since everyday weights and measures are mostly non-SI, children in U.S. public schools are generally taught customary units before SI, although many schools are now attempting to teach SI units at an earlier age.

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In most Commonwealth countries, such as Australia and New Zealand, where metrication has been more forcefully imposed and has encountered less resistance from industry and consumer market forces, metrication is relatively complete, although some informal usage of non-SI units remains, particularly in Canada. Although increasingly metric, the UK has taken some time to change over, and retains use of non-SI units, particularly in informal situations. In more populated and developed British colonies, such as India, existing local weights and measures had been redefined based upon English units; some of which are still in limited use.

Related Topics:
Australia - New Zealand - Canada - India

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Other countries have had customary units of their own, sometimes very similar in root (Germanic, Roman), name and value to the ones listed below—foot or pound, for instance—but frequently, similar terms designate quite different sizes. For example, miles ranged from 1 to 10 kilometers. The standardization of these units was of varying quality, but was often comparable to or better than the U.S. customary system of the 19th century. Most were later redefined in terms of kilogram and meter. Often, unlike English units, they were rounded to "nice" SI values, leading to their use in colloquial speech, alongside SI terms, into the present day.

Related Topics:
Foot - Pound - Mile - Kilogram - Meter

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Historically, a wide range of non-SI units have been used in the United States. and United Kingdom, and in England before that, but many of these have fallen into disuse. This article only deals with the units commonly used or officially defined in the United States.

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