Metrication in the United States

Metrication (or metrification) is the process of introducing the International System of Units (or SI), more commonly known as the metric system, to replace the traditional or customary units of measurement of a country or region. Although all U.S. customary units have been redefined in terms of SI units, the United States does not commonly mandate the use of SI. This, according to the CIA Factbook, makes the United States one of only three countries, as of 2016^[update], with Myanmar (Burma) and Liberia, that have not adopted, or are not in the process of adopting, the metric system as their official system of weights and measures.

Although the Constitution grants Congress the authority to determine standards of measure, it was not until 1832 that the customary system of units was formalized. In the early 19th century, the U.S. Coast and Geodetic Survey (the government's surveying and map-making agency) used meter and kilogram standards brought from France. Shortly after the American Civil War, the 39th United States Congress protected the use of the metric system in commerce with the Metric Act of 1866 and supplied each state with a set of standard metric weights and measures. In 1875, the United States solidified its commitment to the development of the internationally recognized metric system by becoming one of the original seventeen signatory nations to the Metre Convention or the Treaty of the Metre. The signing of this international agreement concluded five years of meetings in which the metric system was reformulated, refining the accuracy of its standards. The Metre Convention established the International Bureau of Weights and Measures (Bureau international des poids et mesures, BIPM) in Sèvres, France, to provide standards of measurement for worldwide use.

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