Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United States

The "Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United States" was a report submitted to the U.S. House of Representatives on July 13, 1790, by Secretary of State Thomas Jefferson.

At the First United States Congress, which met in 1789 when the metric system had not yet been developed in France, the system of units to be used in the future USA was one point of discussion. The Congress had (and still has) the constitutional right (article I, section 8) to decide on a standard of weights and measures. On January 2, 1790, George Washington urged Congress to address the need for the uniform system of weights and measures, and on January 15, 1790, the House of Representatives requested Thomas Jefferson to draw up a plan.

The decimal dollar had already been agreed upon in principle in 1785, but would not be implemented until after passage of the Mint Act in 1792. In mid-1790 Jefferson proposed two systems of units, one evolutionary with a mere refinement of definitions and simplification of the existing English system, the other one revolutionary being decimal and only reusing some of the traditional names. Jefferson's proposal was the world's first scientifically based, fully integrated, decimal system of weights and measures.

In coordination with scientists in France, Jefferson selected the seconds pendulum at 45° latitude as the basic reference. For technical reasons, he proposed using a uniform rod as the pendulum rather than a traditional pendulum. The pendulum was estimated to be 39.14912 English inches long (in the inches of that time—it wasn't until much later that the inch was defined to be 25.4 mm), or 1.5 times that for a vibrating rod (58.72368 inches).

In the evolutionary approach, the foot was to be derived from one of these lengths by a simple integer factor, which would be either three (pendulum) or five (rod), i.e. lengthening it from the traditional value by 1.04970¯6 inches to ca. 331.463 mm or shortening it by 0.255264 inches to ca. 298.317 mm. For practical purposes he wanted the rod to be 58¾ (new) inches long, an increase of less than 0.045%.

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