French units of measurement

France has a unique history of units of measurement due to radical attempts to adopt a metric system following the French Revolution.

In the Ancien régime, before 1795, France used a system of measures that had many of the characteristics of the modern Imperial System of units. 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. In the revolutionary era, France used the first version of the metric system. This system was not well received by the public. Between 1812 and 1837, the mesures usuelles was used – traditional names were restored, but were based on metric units: for example, the livre became 500 g. After 1837, the metric system was reintroduced and has remained the principal system of use to this day.

In the pre-revolutionary era (before 1795), France used a system of measures that had many of the characteristics of the modern Imperial System of units, but there was no unified system of measurement. Charlemagne and successive kings had tried but failed to impose a unified system of measurement in France. (In England, by contrast, the Magna Carta decreed that "there shall be one unit of measure throughout the realm.")

The names and relationships of many units of measure were adopted from Roman units of measure and many more were added – it has been estimated that there were seven or eight hundred different names for the various units of measure. In addition, the quantity associated with each unit of measure differed from town to town and even from trade to trade to such an extent that the lieue (league) could vary from 3.268 km in Beauce to 5.849 km in Provence. It has been estimated that, on the eve of the Revolution, a quarter of a million different units of measure were in use in France. Although certain standards, such as the pied du roi (the king's foot) had a degree of pre-eminence and were used by savants across Europe, many traders chose to use their own measuring devices, giving scope for fraud and hindering commerce and industry.

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