The Metric Conversion Act is an Act of Congress that U.S. President Gerald Ford signed into law on December 23, 1975. It declared the metric system "the preferred system of weights and measures for United States trade and commerce", but permitted the use of United States customary units in all activities. As Ford's statement on the signing of the act emphasizes, all conversion was to be "completely voluntary." The Act also established the United States Metric Board with representatives from scientific, technical, and educational institutions, as well as state and local governments to plan, coordinate, and educate the American people for the Metrication of the United States.
Executive Order 12770, which cites the Metric Conversion Act of 1975, 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."
The metrification board was abolished in 1982 by President Ronald Reagan, largely on the suggestion of Frank Mankiewicz and Lyn Nofziger..
This summary is from Wikipedia.
The summary below was written by the Congressional Research Service, which is a nonpartisan division of the Library of Congress.
12/8/1975--Passed Senate amended.
(Measure passed Senate, amended, in lieu of S. 100) Metric Conversion Act - Establishes the United States Metric Board, composed of 17 members, with a chairman, appointed by the President by and with the advice of the Senate. Requires such members to be representatives of groups and interests including engineers, scientists, manufacturers, retailers, labor, small business, and educators. Directs the Board to carry out a program of planning, coordination and public education to implement the increasing use of the metric system in the United States. Requires the Board in carrying out such program to consider conversion costs, to provide procedures whereby groups may recommend methods of coordinating conversion in various industries, to encourage activities of standardization organizations to develop engineering standards on a metric measurement basis, to cooperate with foreign governments, to assist the public in becoming familiar with the use of metric terms and measures, to report annually to the Congress on its activities, and to submit to the Congress and to the President, not later than one year after the date of enactment of the Act authorizing appropriations for this Act, a report on the need to provide an effective structural mechanism for converting customary units to metric units in statutes, regulations, and other laws at all levels of government. Authorizes necessary appropriations to carry out the provisions of this Act.