Act to authorize the use of the metric system of weights and measures
The act of 1866 legalized the metric system of weights and measures in the United States. Passed on July 28, 1866, the act as follows:
Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, that from and after the passage of this act it shall be lawful throughout the United States of America to employ the weights and measures of the metric system; and no contract or dealing, or pleading in any court, shall be deemed invalid or liable to objection because the weights or measures expressed or referred to therein are weights or measures of the metric system.
Sec 2: And be it further enacted that the tables in the schedule hereto annexed shall be recognized in the construction of contracts, and in all legal proceedings, as establishing, in terms of the weights and measures now in use in the United States, the equivalents of the weights and measures expressed therein in terms of the metric system; and said tables may be lawfully used for computing, determining, and expressing in customary weights and measures the weights and measures of the metric system.
HR 596 Metric Law, “An Act to authorize the use of the metric system of weights and measures,” from the 39th Congress in 1866.