Before the Revolution French units of measurement were based on the Carolingian system, introduced by the first Holy Roman Emperor Charlemagne (800 – 814 AD) which in turn were based on ancient Roman measures. Charlemagne brought a consistent system on measures across the entire empire. However, after his death the empire fragmented and many rulers introduced their own variants of the units of measure.
Some of Charlemagne’s units of measure, such as the pied du roi (the king’s foot) remained virtually unchanged for about a thousand years, while others, such as the aune (ell - used to measure cloth) and the livre (pound) varied dramatically from locality to locality. By the time of the revolution, the number of units of measure had grown to the extent that it was almost impossible to keep track to them.
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Although the pre-revolutionary era (before 1795) when France used a system of measures that had many of the characteristics of the modern Imperial System of units, there was no unified system of measurement in France. Whereas in England the Magna Carta decreed that "there shall be one unit of measure throughout the realm", Charlemagne and successive kings had tried but failed to impose a unified system of measurement in France.[1]
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. Moreover the quantity associated with each unit of measure differed from town to town and even from trade to trade to the 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.[2] Although certain standards, such as the pied du roi (the King's foot) had a degree of pre-eminence and were used by savants, many traders chose to use their own measuring devices giving scope for fraud and hindering commerce and industry.[1]
As an example, the weights and measures used at Pernes-les-Fontaines in south eastern France differ from those catalogued later in this article as having been used in Paris. In many cases the names are different, while the livre is shown as being 403 g, as opposed to 489 g - the value of the livre du roi.
These definitions use the Paris definitions for the coutume of Paris,[3] and definitions for other Ancien régime civil jurisdictions varied, at times quite significantly.
The mediaeval royal units of length were based on the toise and in particular the toise de l'Écritoire, the distance between the fingertips of the outstretched arms of a man which was introduced in 790 AD by Charlemagne.[4] The toise has 6 pied (feet) each of 326.6 mm (12.86 in). In 1668 the reference standard was found to have been deformed and it was replaced by the toise du Châtelet which, to accommodate the deformation of the earlier standard, was 11 mm (0.55 %) shorter.[5] In 1747 this toise was replaced by a new toise of near-identical length - the Toise du Pérou, custody of which was given to l'Académie des Sciences au Louvre.[6]
Although the pouce (inch), pied (foot) and toise were fairly consistent throughout most of pre-revolutuionary France, some areas had local variants of the toise. Other units of measure such as the aune (ell), the perche (perch/rood), the arpent and the lieue (league) had a number of variations, particularly the aune (which was used to measure cloth[7]
The loi du 19 frimaire an VIII (Law of 10 December 1799) states that one decimal metre is exactly 443.296 French lines, or 3 pieds 11.296 lignes de la "Toise du Pérou".[8] Thus the French royal foot is exactly 9000/27706 metres ( about 0.3248 m).[9]
In Quebec, the surveys in French units were converted using the relationship 1 pied (of the French variety, the same word being used for English feet as well) = 12.789 English inches.[10] This makes the Quebec pied very slightly smaller (about 4 parts in one million) than the pied used in France.
| 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 de 25 au degré | ~13,692 | ~4.448 km | ~2.764 miles | Linked to the circumference of the Earth, with 25 lieues making up one degree of a great circle. It was measured by Picard in 1669 to be 2282 toises. | |
| 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 | ||
| 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. | |
| 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 | ~1/2 pint | Etymologically, 'demi' in French means 'half', in this case, half a chopine, and - conveniently - also half a (US) pint. | |
| chopine | 1/2 | ~476.1 ml | ~1 pint | ~0.84 pint | |
| pinte | 1 | ~952.1 ml | ~2.01 pint | ~1.68 pint | 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 | ~1/2 gallon | ~0.42 gallon | |
| velte | 8 | ~7.617 L | ~2.01 gallon | ~1.68 gallon | |
| 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. | ||
| Table of (dry) volume units | |||||
|---|---|---|---|---|---|
| Unit | Relative value |
SI value |
imperial value |
U.S. value |
Notes |
| litron | 1⁄16 | 793.5 mL | 0.1745 imp gal | 0.1801 US dry gal | The litre is etymologically related to this unit. |
| quart | 1⁄4 | 3.174 L | 0.698 imp gal | 0.721 US dry gal | |
| boisseau | 1 | 12.7 L | 2.8 imp gal | 2.9 US dry gal | A boisseau was defined as 10⁄27 of a French cubic foot. |
| minot | 3 | 38.09 L | 8.38 imp gal | 8.65 US dry gal | |
| mine | 6 | 76.17 L | 16.76 imp gal | 17.29 US dry gal | |
| setier | 12 | 152.3 L | 33.5 imp gal | 34.6 US dry gal | |
| muid | 144 | 1,828 L | 402 imp gal | 415 US dry gal | |
| cubic | |||||
| pouce cube | 1⁄640 | ~19.84 cm3 | ~1.211 cu in | This is the French cubic inch. | |
| pied cube | 2.7 | ~34.28 dm3 | ~2,092 cu in | This is the French cubic foot. | |
According to the law of 19 Frimaire An VIII (December 10, 1799),
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 | ||
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