Metrication in the United States
is the process of introducing what is now the International System of Units, also known as SI units, to replace a jurisdiction's traditional measuring units. U.S. customary units have been defined in terms of metric units since the 19th century, and, according to United States law, the SI has been the "preferred system of weights and measures for United States trade and commerce" since 1975.
The U.S. has a national policy to adopt the metric system. Under Executive Order 12770, signed in 1991 by President George H.W. Bush, all U.S. agencies were required to adopt the metric system. However, conversion was made not mandatory, so U.S. customary units remain in common use in government and in many industries. There is government policy and metric program to implement and assist with metrication, but there is strong social resistance to further metrication.
In three important domains, cooking/baking, and distance and temperature measurement, customary units are generally used rather than metric.
However, the SI is used extensively in fields such as science, medicine, electronics, the military, automobile production and repair, and international affairs. The U.S. uses metric measures in photography, medicine, nutrition labels, bottles of soft drink, and volume displacement in engines.
The scientific and medical communities use metric units almost exclusively, as does NASA. All aircraft and air traffic control use only Celsius temperature at US airports and while in flight. Post-1994 federal law also mandates most packaged consumer goods be labeled in both customary and metric units. The U.S. has fully adopted the second, the SI unit for time.
History
18th century
Immediately after gaining independence from Great Britain, the United States used a variety of units of measure, including Dutch units and English units. The 1789 Constitution grants Congress the authority to determine standards of measure, though it did not immediately use this authority to impose a uniform system. The United States was one of the first nations to adopt a decimal currency, under the Coinage Act of 1792.In 1793, Thomas Jefferson requested equipment from France that could be used to evaluate the metric system within the United States. Joseph Dombey returned from France with a standard kilogram. Before reaching the United States, Dombey's ship was blown off course by a storm and captured by pirates, or strictly privateers in the Caribbean, he died in captivity on Montserrat.
19th century
In 1832, 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 a physical meter standard, the "Committee Meter", brought from Switzerland. 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, also known as 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 in Sèvres, France, to provide standards of measurement for worldwide use.
Under the Mendenhall Order of 1893, metric standards, developed through international cooperation under the auspices of BIPM, were officially adopted as the fundamental standards for length and mass in the United States, though some metric standards were used in practice before then. The definitions of United States customary units, such as the foot and pound, have been based on metric units since then.
The 1895 Constitution of Utah, in Article X, Section 11, originally mandated that: "The Metric System shall be taught in the public schools of the State." This section was repealed, effective July 1, 1987.
On July 4, 1876, Melvil Dewey incorporated the American Metric Bureau in Boston to sell rulers and other metric measuring tools. Dewey had hoped to make his fortune selling metric supplies.
20th century
The General Conference on Weights and Measures is the governing body for the modern metric system and comprises the signing nations of the Treaty of the Metre. The General Conference on Weights and Measures approved an updated version of the metric system in 1960 named Le Système international d'unités and abbreviated SI.On February 10, 1964, the National Bureau of Standards issued a statement that it would use the metric system, except where this would have an obvious detrimental effect.
In 1968, Congress authorized the U.S. Metric Study, a three-year study of systems of measurement in the United States, with emphasis on the feasibility of metrication. The United States Department of Commerce conducted the study. A 45-member advisory panel consulted and took testimony from hundreds of consumers, business organizations, labor groups, manufacturers, and state and local officials. The final report of the study concluded that the U.S. would eventually join the rest of the world in the use of the metric system of measurement. The study found that metric units were already implemented in many areas and that their use was increasing. The majority of study participants believed that conversion to the metric system was in the best interests of the United States, particularly in view of the importance of foreign trade and the increasing influence of technology in the United States.
The U.S. Metric Study recommended that the United States implement a carefully planned transition to the principal use of the metric system over a decade. Congress passed the Metric Conversion Act of 1975 "to coordinate and plan the increasing use of the metric system in the United States". Voluntary conversion was initiated, and the United States Metric Board was established for planning, coordination, and public education. The public education component led to public awareness of the metric system, but the public response included resistance, apathy, and confusion. In 1981, the USMB reported to Congress that it lacked the clear Congressional mandate necessary to bring about national conversion. Because of this ineffectiveness and an effort of the Reagan administration—particularly from Lyn Nofziger's efforts as a White House advisor to the Reagan administration, to reduce federal spending—the USMB was disbanded in the autumn of 1982.
The ending of the USMB increased doubts that metrication would really be implemented. Public and private sector metrication slowed even while competitiveness between nations and demands of global marketplaces increased.
The American National Metric Council was established in 1973 by the American National Standards Institute as a non-profit, tax-exempt organization for planning and coordinating metric activity in all sectors of the U.S. economy. The ANMC became a separately incorporated organization in 1976. The ANMC was intended to facilitate U.S. metrication by maintaining a voluntary and orderly process that minimizes costs and maximizes benefits, and to provide information, forums, individual assistance, and other services for its subscribers.
The ANMC attempted to coordinate the metric planning of many industrial sectors, unlike the USMB, which only attempted to implement the policy set forth in the Metric Conversion Act of 1975. After the formation of the USMB, committees of the ANMC submitted conversion plans for the chemical sector and for the instruments sector. These sector conversion plans were later approved by the USMB. From 1975 through 1987, the ANMC held a series of well-attended annual conferences. Subsequently, a series of National Metric Conferences, jointly sponsored by the ANMC, the U.S. Metric Association, the Department of Commerce, and the National Institute of Standards and Technology, were held from 1989 through 1993.
National Metric Week, begun by the National Council of Teachers of Mathematics, was first held in 1976 during the week beginning on May 10. It continued to occur in May, although not always including the day May 10, until 1983, when it was moved to the week of October 10. This was because the original date was considered too
near to the school year ending.
Congress included new encouragement for U.S. industrial metrication in the Omnibus Foreign Trade and Competitiveness Act of 1988. This legislation amended the Metric Conversion Act of 1975 and designated the metric system as "the Preferred system of weights and measures for United States trade and commerce". The legislation states that the federal government has a responsibility to assist industry, especially small business, as it voluntarily converts to the metric system of measurement. The legislation required most federal agencies to use the metric system in their procurement, grants, and other business-related activities by the end of 1992.
While not mandating metric use in the private sector, the federal government has sought to serve as a catalyst in the metric conversion of the country's trade, industry, and commerce. Exceptions were made for the highway and construction industries. The Department of Transportation planned to require metric units by 2000, but this plan was canceled by the 1998 highway bill TEA21. The U.S. military has generally high use of the metric system, partly because of the need to work with other nations' militaries.
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, which will assist the Secretary in coordinating Federal Government-wide implementation of this order."
Some members of Congress attempted to ban use of the metric system on federal highways in 1992 and 1993. These bills were not popular in the House of Representatives and failed before a vote.
The use of two different unit systems caused the loss of the Mars Climate Orbiter on September 23, 1999. NASA specified metric units in the contract. NASA and other organizations applied metric units in their work, but one subcontractor, Lockheed Martin, provided software that calculated and reported thruster performance data to the team in pound-force-seconds, rather than the expected newton-seconds. The spacecraft was intended to orbit Mars at about altitude, but incorrect data caused it to descend instead to about, presumably burning up in the Martian atmosphere.