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Before the French Revolution, which started in 1789, 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 of 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 of them.
Although in the pre-revolutionary era (before 1795) France used a system and units of measure that had many of the characteristics of contemporary English units (or the later Imperial System of units), France still lacked a unified, countrywide system of measurement. 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.
The names and relationships of many units of measure were adopted from Roman units of measure and much 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. 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.
Tables of units of measure
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. The toise had 6 pieds (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. 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.
Although the pouce (inch), pied (foot) and toise (fathom) were fairly consistent throughout most of pre-revolutionary France, some areas had local variants of the toise. Other units of measure such as the aune (ell), the perche (perch or rood), the arpent and the lieue (league) had a number of variations, particularly the aune (which was used to measure cloth).
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". Thus the French royal foot is exactly 9,000/ metres (about 0.3248 m).
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. This makes the Quebec pied very slightly smaller (about 4 parts in one million) than the pied used in France.
|point||1⁄1728||~0.188 mm||~7.401 thou||1⁄12 of a ligne. This unit is usually called the Truchet point in English.|
|ligne||1⁄144||~2.256 mm||~88.81 thou||1⁄12 of a pouce. This corresponds to the line, a traditional English unit.|
|pouce||1⁄12||~27.07 mm||~1.066 in||1⁄12 of a pied du roi. 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. Known in English as the Paris foot (properly a separate, shorter unit), the royal foot, or French foot.|
|toise||6||~1.949 m||~6.394 ft, or
|Six pieds du roi. This corresponds to the fathom, a traditional English unit. Unlike the fathom, it was used in both land and sea contexts.|
|perche d'arpent||22||~7.146 m||~7.815 yd||Related to, but not directly corresponding with, the English perch or rod (which is 16 1⁄2 feet, approximately three-quarters of the French perche).|
|arpent||220||~71.46 m||~78.15 yd||Ten perches.|
|lieue ancienne||10,000||~3.248 km||~2.018 miles||This is an old French league, defined as 10,000 (a myriad) pieds. It was the official league in parts of France until 1674.|
|lieue de Paris||12,000||~3.898 km||~2.422 miles||This league was defined in 1674 as exactly 2,000 toises. After 1737, it was also called the "league of bridges and roads" (lieue des Ponts et des Chaussées).|
|lieue des Postes||13,200||~4.288 km||~2.664 miles||This league is 2,200 toises or 60 arpents. 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. (Compare the international nautical mile, of which 60 make one degree; one lieue therefore equaling 2.4 nautical miles.) It was measured by Picard in 1669 to be 2,282 toises.|
|lieue tarifaire||14,400||~4.678 km||~2.907 miles||This league is 2,400 toises. It was created in 1737.|
|perche du roi||18||~5.847 m||~6.394 yd||This perch was used in Quebec and Louisiana|
|arpent (du roi)||180||~58.47 m||~63.94 yd||Ten perches du roi.|
|perche ordinaire||20||~6.497 m||~7.105 yd||This perch was used locally.|
|arpent (ordinaire)||200||~64.97 m||~71.05 yd||Ten perches ordinaires.|
- The French typographic point, the Didot point, was 1⁄72 of a French inch, i.e. two royal points. The French pica, called Cicéro, measured 12 Didot points or 1⁄6 inch.
|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.|
|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 pieds du roi on each side.|
|vergée||12,100||~1277 m2||~1527 sq yd||This is a square 5 perches on each side, or one quarter of an acre.|
|48,400||~5107 m2||~6108 sq yd, or
|The French acre is a square 10 perches (one arpent) on each side. (Does not exactly correspond to the English acre, which is defined as 43,560 square feet.)|
|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 pieds du roi on each side.|
|vergée (du roi)||8,100||~854.7 m2||~1022 sq yd||This is a square 5 perches du roi on each side.|
|acre (du roi), or
|32,400||~3419 m2||~4089 sq yd, or
|This acre is a square 10 perches du roi on each side. Certain U.S. states have their own official definitions for the (square) arpent, which vary slightly from this value.|
|perche (ordinaire) carrée||400||~42.21 m2||~50.48 sq yd||This square perch was used locally. It is a square 20 pieds du roi on each side.|
|vergée (ordinaire)||10,000||~1055 m2||~1262 sq yd||This is a square 5 perches ordinaires on each side.|
|acre (ordinaire), or
|40,000||~4221 m2||~5048 sq yd, or
|This acre is a square 10 perches ordinaires on each side.|
Volume – liquid measures
|roquille||1⁄32||~29.75 ml||One quarter of a posson.|
|demiard||1⁄4||~238 ml||~0.5 pint||Etymologically, demi in French means "half": in this case, half a chopine, and – coincidentally – also approximately 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 pied du roi.|
|quade||2||~1.904 L||~0.5 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, or two cubic pieds du roi.|
|muid||288||~274.2 L||The muid is defined as eight cubic pieds du roi.|
|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.|
Volume – dry measures
|litron||1⁄16||793.5 mL||0.1745 imp gal||0.1801 U.S. dry gal||1⁄4 of a quart. The litre is etymologically related to this unit.|
|quart||1⁄4||3.174 L||0.698 imp gal||0.721 U.S. dry gal||1⁄4 of a boisseau.|
|boisseau||1||12.7 L||2.8 imp gal||2.9 U.S. dry gal||Although etymologically related to the English unit bushel, the French bushel is about one third the size. A boisseau was defined as 10⁄27 of a cubic pied du roi.|
|minot||3||38.09 L||8.38 imp gal||8.65 U.S. dry gal|
|mine||6||76.17 L||16.76 imp gal||17.29 U.S. dry gal|
|setier||12||152.3 L||33.5 imp gal||34.6 U.S. dry gal|
|muid||144||1,828 L||402 imp gal||415 U.S. dry gal|
|pouce cube||1⁄640||~19.84 cm3||~1.211 cu in||This is the French cubic inch.|
|pied cube||2 7⁄10||~34.28 dm3||~2,092 cu in||This is the French cubic foot. Exactly 2.7 boisseaux.|
|one quintal (100 livres) poids de table / poids de ville in||poids de marc equivalent (livres, approximations per source)|
|Rouen (poids de vicomté)||103|
|Strasbourg (petit poids)||96|
|nominal (marcs)||error in actual (grains)|
Charlemagne's system had 12 onces (ounces) to the livre (pound). Between 1076 and 1093 King Philip I instituted a system of poids de marc (mark weight) used for minting coin, with 8 onces to a marc.
King Jean II constructed a new standard of measures, including a livre actuelle ("current" pound, also known as a livre de poids de marc or "mark weight" pound) of 2 marcs, i.e. 16 onces. The Charlemagne 12-ounce livre became known as the livre esterlin ("true" pound) in order to distinguish it. "esterlin" was a Middle French word that did not survive into Modern French.
The livre actuelle could be sub-divided into 2 demi-livres (half-pounds), 4 quarterons, or 8 demi-quarterons. Conversely, there were 100 livres in a quintal (c.f. English hundredweight). The fractional parts of an once had different names in Apothecary measure (used in medicine) and measure of precious metals, but the fractional ratios were themselves the same: 1 once was 8 drachme (Apothecary, c.f. English dram) or gros; 1 drachme/gros was 3 scruples (Apothecary, c.f. English scruple) or deniers, and 1 scruple/denier was 24 grains. This makes 384 deniers in a livre in weight measure, which contrasts with the old monetary livre in France which was divided into 240 deniers.
Jean II's standards are preserved in the Conservatoire Nationale des Arts et Métiers, which also holds a set of later-still physical standards from the 15th century, the so-called pile de Charlemagne. This pile defined the weight of 50 marcs, i.e. 400 onces, and thus 25 livres actuelles, or 33⅓ livres esterlins. It had been kept in the royal palaces originally. In 1540 King François I had transferred it to the Cour des monnaies, where it had been held in a cabinet with three locks, whose keys had been held separately by the president of the Cour, one of its counsellors, and a clerk.
The thirteen individual pieces that made up the Parisian pile de Charlemagne comprised an outer containing cylinder nominally weighing 20 marcs, and a set of hollow nesting cups within, topped with a filled weight as the smallest piece. The heaviest cups were nominally 14, 8, 4, and 2 marcs, sub-totalling 48 marcs; followed by a nominally 1 marc hollow cup which was termed the marc creux (hollow mark); and followed by 6 further cups (4, 2, and 1 onces, and 4, 2, and 1 gros) with a final seventh filled 1 gros weight, all totalling 1 marc, which was termed the marc plein (filled mark).
Unfortunately, the weights were not consistent, with the marc plein not being the same weight as the marc creux, and neither being the same as a mean 1 marc weight determined from the weight of the whole pile. So when the time came to work out the conversion factors between these measures and the metric system, the whole pile was taken to define 50 Parisian standard marcs, and thus 230400 grains (the number of grains in 50 marcs).Louis Lefèvre‑Gineau initially determined that the metric mass of the whole pile was 12.2279475kg, later corrected to 12.2376kg, thereby making (by division and rounded to three decimal places) a marc 244.753g, a livre esterlin 367.129g, and a livre actuelle 489.506g. Hence further the (Parisian) once was 30.594g, the gros/drachme was 3.824g, the denier/scruple was 1.274g, and the grain was 0.053g.
However, the actual masses of the pre-metric measures were nowhere near even this simple. These were just the Parisian standards, and individual provinces, cities, and even guilds, all had their own reference physical standards, which were not checked against one another and which sometimes conflated esterlin and actuelle. For just some examples: the Marseille livre was 399.6g, the Montpelier one 394.9g, the Toulon one 465.5g, and the Toulouse one 413.2g; with all of the fractional subdivisions having different values accordingly. The Limoges marc was 240.929g, the Tours one 237.869g, and the Troyes one 250.050g.
Furthermore, there were also livres comprising different numbers of onces to both the actuelle and esterlin, including livres of 14, 18, and 20 onces, confusing things yet further. The livre in the poids de table (table weight) systems used in Provence and Languedoc (and a common name for provincial weight systems in general alongside poids de pays, country weight, and poids de ville, town weight) was the same weight as 15 onces or even as low as 13 onces in the Parisian poids de marc, and the livre in the poids de soie (silk weight) system of Lyon was similarly just 15⁄16 the weight of the Parisian livre. This caused an erroneous belief that these livres comprised 13, 14, or 15 onces, however this was a confusion stemming from the equivalent poids de marc weights, and both poids de table and poids de soie had 16 of their own, lighter, onces and so forth, Rouen had a poids de vicomté system.
- "History of measurement". Métrologie française. Retrieved 2011-02-06.
- Adler 2002, pp. 2–3.
- See far: Droit couturier en France.
- Sabot 2000.
- Darcy-Bertuletti 2005.
- This can be shown by noting that 27,706 × 16 = 443,296 and that 9 × 16 = 144, the number of lignes in a pied.
- Weights and Measures Act, Schedule III
- Expilly 1768, p. 712.
- Harkness 1888, p. lix.
- Saigey 1834, p. 114.
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