Units of measurement in France

France has a unique history of units of measurement due to its radical decision to invent and adopt the metric system after the French Revolution.

Woodcut dated 1800 illustrating the new decimal units which became the legal norm across all France on 4 November 1800
Table of the measuring units used in the 17th century at Pernes-les-Fontaines in the covered market at Provence-Alpes-Côte d'Azur region of southeastern France

In the Ancien régime and until 1795, France used a system of measures that had many of the characteristics of the modern Imperial System of units but with no unified system. There was widespread abuse of the king's standards, to the extent that the lieue could vary from 3.268 km in Beauce to 5.849 km in Provence. During the revolutionary era and motivated in part by the inhomegeneity of the old system, France switched to the first version of the metric system. This system was not well received by the public, and between 1812 and 1837, the country used the mesures usuelles – traditional names were restored, but the corresponding quantities were based on metric units: for example, the livre (pound) became exactly 500 g. After 1837, the metric system was reintroduced and progressively became the only system of use, with other units now in only residual use.

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