Who came up with the metric system in 1790?

Answer 1

The year presupposed by the question is not really correct.

During the early years of the French Revolution, the leaders of the French revolutionary Assemblée Constituante decided that rather than standardising the size of the existing units, they would introduce a completely new system based on the principles of logic and natural phenomena.

Initially France attempted to work with other countries towards the adoption of a common set of units of measure. Among the supporters of such an international system of units was Thomas Jefferson who, in 1790, presented a document Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United States to congress in which he advocated a decimal system that used traditional names for units (such as ten inches per foot). The report was considered but not adopted by Congress. There was little support from other countries.

Then, France started the ball rolling by passing the law of 18 Germinal, Year III (7 April 1795) which defined five units of measure (including metre, litre and gram). France officially adopted the metric system on 10 December 1799 with conversion being mandatory first in Paris and then across the provinces.

Answer 2

The French Academy of Sciences played a significant role in the development of the metric system in 1790. The system was later formally adopted by the French National Assembly in 1795.