French units of measurement

French units of measurement

In France, before the decimalised metric system of 1799, a well-defined old system existed, however with some local variants. For instance, the "lieue" could vary from 3.268 km in Beauce to 5.849 km in Provence. Between 1812 and 1839, many of the traditional units continued in "metrified" adaptations as the "mesures usuelles".


The French law for the definitive metre of 1799 states that one decimal metre is exactly 443.296 French lines, or 3 French feet, 0 French inches and 11.296 French lines. The French royal foot is exactly 9000/27706 metres, or about 0.3248 metres. [ fr icon]

In Quebec, the surveys in French units were converted using the relationship 1 "pied" (of the French variety; the same word is used for English feet as well) = 12.789 English inches. [ [ Weights and Measures Act, Schedule III] ] This makes the Quebec "pied" very slightly smaller (about 4 parts in one million) than the "pied" used in France.

This article uses the Paris definitions, although the difference is not significant for the level of precision available at the time. In addition, the changing definitions of the metric units since 1799 means that even the precise relationship between French feet and metres may no longer be so accurate.

Dry measures


According to the law of 19 Frimaire An VIII (December 10, 1799),

* The kilogramme is equal to 18,827.15 grains. The kilogramme is, in addition, defined as the weight of 1 dm³ of distilled water at 4 degrees centigrade, i.e. at maximum density. [ fr icon]

Traditionally, the French pound ("livre") was defined as the mass of exactly frac|70 of a French cubic foot of water. When the kilogramme was defined, knowledge that a "pied du roi cube" filled with water masses exactly 70 French pounds was apparently lost. According to the traditional (cubic foot) definition, one "livre" would have been about 489.675 grammes. According to the kilogramme definition, one "livre" was about 489.506 grammes. The difference is about 0.035%. However, a small difference in salinity (i.e. the difference between distilled water and very good quality drinking water) is enough to explain this difference.

The units in the following table are (except for the talent) calculated based on the kilogramme definition of the "livre".

See also

* Weights and measures
* Systems of measurement
* Mesures usuelles
* SI
* Jean-Antoine Chaptal
* Réaumur scale


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