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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.
Contents
1Length
2Area
3Volume
3.1Liquid measures
3.2Dry measures
4Mass
5See also
6References
Length
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. [1]
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.[citation needed] This makes the Quebec pied very slightly smaller (about 4 parts in one million) than the pied used in France.
This page 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.
The French typographic point, the Didot point, was 1/72 French inches, i.e. two royal points. The French pica, called Cicéro, measured 12 Didot points.
Area
Table of area units
Unit
Relative value
Metric value
Imperial value
Notes
pied carré
1
~1055 cm²
~1.136 sq ft
This is the French square foot.
toise carrée
36
~3.799 m²
~40.889 sq ft, or ~4.543 sq yd
This is the French square fathom.
Paris
perche d'arpent carrée
484
~51.07 m²
~61.08 sq yd
This was the main square perch in old French surveying. It is a square 22 feet on each side.
The French acre is a square 10 perches on each side.
North America
perche du roi carrée
324
~34.19 m²
~40.89 sq yd
This square perch was used in Quebec and Louisiana. It is a square 18 feet on each side.
vergée
8,100
~854.7 m²
~1022 sq yd
This is a square 5 perches on each side.
acre, or arpent carré
32,400
~3419 m²
~4089 sq yd, or ~0.8448 acres
This acre is a square 10 perches on each side. Certain U.S. states have their own official definitions for the (square) arpent, which vary slightly from this value.
Local
perche (ordinaire) carrée
400
~42.21 m²
~50.48 sq yd
This square perch was used locally. It is a square 20 feet on each side.
Although etymologically related to the English unit pint, the French pint is about twice as large. It was the main small unit in common use, and measured 1/36 of a cubic French foot.
quade
2
~1.904 L
velte
8
~7.617 L
quartaut
72
~68.55 L
A quartaut is 9 veltes.
feuillette
144
~137.1 L
muid
288
~274.2 L
The muid is defined as eight French cubic feet.
cubic
pouce cube
1/48
~19.84 ml
This is the French cubic inch.
pied cube
36
~34.28 L
This is the French cubic foot. In ancient times, a cubic foot was also known as an amphora when measuring liquid volume.
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. [2]
Traditionally, the French pound (livre) was defined as exactly 1/70 of a French cubic foot. When the kilogramme was defined, knowledge that a pied du roi cube filled with water masses exactly 70 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.
This is the mass of one French cubic foot of water; this value is calculated based on the French cubic foot and an assumed water density of 1 g/cm³; other values in this table are based off the kilogramme definition.
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