French units of measurement
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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.
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[edit] 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. [2] 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.
| Table of length units | |||||
|---|---|---|---|---|---|
| Unit | Relative value |
SI value |
Imperial value |
Notes | |
| point | 1/12³ | ~0.188 mm | ~7.401 thou | This unit is usually called the Truchet point in English. | |
| ligne | 1/12² | ~2.256 mm | ~88.81 thou | This corresponds to the line, a traditional English unit. | |
| pouce | 1/12 | ~27.07 mm | ~1.066 in | This corresponds to the inch, a traditional English unit. | |
| pied du roi | 1 | ~32.48 cm | ~1.066 ft | Commonly abbreviated to 'Pied', this corresponds to the foot, a traditional English unit. | |
| toise | 6 | ~1.949 m | ~6.394 ft, or ~2.131 yd |
This corresponds to the fathom, a traditional English unit. Unlike the fathom, it was used in both land and sea contexts. | |
| Paris | |||||
| perche d'arpent | 22 | ~7.146 m | ~7.815 yd | ||
| arpent | 220 | ~71.46 m | ~78.15 yd | ||
| lieue ancienne | 10,000 | ~3.248 km | ~2.018 miles | This is the old French league, defined as 10,000 (a myriad) feet. It was the official league until 1674. | |
| lieue de Paris | 12,000 | ~3.898 km | ~2.422 miles | This league was defined in 1674 as exactly 2000 toises. After 1737, it was also called the "league of bridges and roads" (des Ponts et des Chaussées). | |
| lieue des Postes | 13,200 | ~4.288 km | ~2.664 miles | This league is 2200 toises. It was created in 1737. | |
| lieue tarifaire | 14,400 | ~4.678 km | ~2.907 miles | This league is 2400 toises. It was created in 1737. | |
| North America | |||||
| perche du roi | 18 | ~5.847 m | ~6.394 yd | This perch was used in Quebec and Louisiana | |
| arpent | 180 | ~58.47 m | ~63.94 yd | ||
| Local | |||||
| perche ordinaire | 20 | ~6.497 m | ~7.105 yd | This perch was used locally. | |
| arpent | 200 | ~64.97 m | ~71.05 yd | ||
- 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.
[edit] Area
| Table of area units | |||||
|---|---|---|---|---|---|
| Unit | Relative value |
SI 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. | |
| vergée | 12,100 | ~1277 m² | ~1527 sq yd | This is a square 5 perches on each side. | |
| acre, or arpent carré |
48,400 | ~5107 m² | ~6108 sq yd, or ~1.262 acres |
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. | |
| vergée | 10,000 | ~1055 m² | ~1262 sq yd | This is a square 5 perches on each side. | |
| acre, or arpent carré |
40,000 | ~4221 m² | ~5048 sq yd, or ~1.043 acres |
This acre is a square 10 perches on each side. | |
[edit] Volume
[edit] Liquid measures
| Table of (liquid) volume units | |||||
|---|---|---|---|---|---|
| Unit | Relative value |
SI value |
U.S. value |
Imperial value |
Notes |
| roquille | 1/32 | ~29.75 ml | |||
| posson | 1/8 | ~119 ml | |||
| demiard | 1/4 | ~238 ml | |||
| chopine | 1/2 | ~476.1 ml | |||
| pinte | 1 | ~952.1 ml | 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. | ||
[edit] Dry measures
| Table of (dry) volume units | |||||
|---|---|---|---|---|---|
| Unit | Relative value |
SI value |
U.S. value |
Notes | |
| litron | 1/16 | ~793.5 ml | The SI unit litre is etymologically related to this unit. | ||
| quart | 1/4 | ~3.174 L | |||
| boisseau | 1 | ~12.7 L | A boisseau was defined as 10/27 of a French cubic foot. | ||
| minot | 3 | ~38.09 L | |||
| mine | 6 | ~76.17 L | |||
| setier | 12 | ~152.3 L | |||
| muid | 144 | ~1828 L | |||
| cubic | |||||
| pouce cube | 1/640 | ~19.84 ml | This is the French cubic inch. | ||
| pied cube | 2.7 | ~34.28 L | This is the French cubic foot. | ||
[edit] Mass
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. [3]
Traditionally, the French pound (livre) was defined as the mass of exactly 1⁄70 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.
| Table of mass units | |||||
|---|---|---|---|---|---|
| Unit | Relative value |
SI value |
Imperial value |
Notes | |
| Poids de marc, mid 14th – late 18th century | |||||
| prime | 1/24³ once | ~2.213 mg | |||
| grain | 1/24² once | ~53.11 mg | ~0.8197 grains | This is the French grain. | |
| denier | 1/24 once | ~1.275 g | ~19.67 grains | ||
| gros | 1/8 once | ~3.824 g | ~2.158 dr | ||
| once | 1/16 | ~30.59 g | ~1.079 oz | This is the French ounce. | |
| marc | 1/2 | ~244.8 g | ~8.633 oz | ||
| livre | 1 | ~489.5 g | ~1.079 lb | This is the French pound. | |
| quintal | 100 | ~48.95 kg | ~107.9 lb | This is the French hundredweight. | |
| talent | |||||
| talent | ~70.02 | ~34.28 kg | ~75.57 lb | 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 on the kilogramme definition. | |
| bullion | |||||
| felin | 1/1280 | ~382.4 mg | ~5.902 grains | ||
| maille | 1/640 | ~764.9 mg | ~11.8 grains | ||
| estelin | 1/320 | ~1.53 g | ~23.61 grains | ||
[edit] See also
[edit] References
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