United States customary units
History

The United States system of units of 1832 is based on the system in use in Britain prior to the introduction to the British imperial system on January 1, 1826. Both systems are derived from English units, a system which had evolved over the millennia before American independence, and which had its roots in both Roman and Anglo-Saxon units.

The customary system was championed by the U.S.-based International Institute for Preserving and Perfecting Weights and Measures in the late 19th century. Some advocates of the customary system saw the French Revolutionary, or metric, system as atheistic. The president of an Ohio auxiliary of the Institute wrote that the traditional units were "a just weight and a just measure, which alone are acceptable to the Lord". His organization later went so far as to publish music for a song proclaiming "down with every 'metric' scheme".

The U.S. government passed the Metric Conversion Act of 1975, which made the metric system "the preferred system of weights and measures for U.S. trade and commerce". The legislation states that the federal government has a responsibility to assist industry as it voluntarily converts to the metric system, i.e., metrification. This is most evident in U.S. labeling requirements on food products, where SI units are almost always presented alongside customary units. According to the CIA World Factbook, the United States is one of three nations (along with Liberia and Myanmar (Burma)) that have not adopted the metric system as their official system of weights and measures.

Executive Order 12770, signed by President George H. W. Bush on July 25, 1991, citing the Metric Conversion Act, directed departments and agencies within the executive branch of the United States Government to "take all appropriate measures within their authority" to use the metric system "as the preferred system of weights and measures for United States trade and commerce" and authorized the Secretary of Commerce "to charter an Interagency Council on Metric Policy ('ICMP'), which will assist the Secretary in coordinating Federal Government-wide implementation of this order."

U.S. customary units are widely used on consumer products and in industrial manufacturing. Metric units are standard in science, medicine, as well as many sectors of industry and government, including the military. There are anecdotal objections to the use of metric units in carpentry and the building trades, on the basis that it is easier to remember an integer number of inches plus a fraction than a measurement in millimeters, or that foot-inch measurements are more suitable when distances are frequently divided into halves, thirds, and quarters, often in parallel. The metric system also lacks a parallel measurement to the foot.

The term "United States customary units" was used by the former United States National Bureau of Standards, although "English units" is sometimes used in colloquial speech.
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