The traditional French units of measurement prior to metrication were established under Charlemagne during the Carolingian Renaissance. Based on contemporary Byzantine and ancient Roman measures, the system established some consistency across his empire but, after his death, the empire fragmented and subsequent rulers and various localities introduced their own variants. Some of Charlemagne's units, such as the king's foot () remained virtually unchanged for about a thousand years, while others important to commercesuch as the French ell () used for cloth and the French pound () used for amountsvaried dramatically from locality to locality. By the 18th century, the number of units of measure had grown to the extent that it was almost impossible to keep track of them and one of the major legacies of the French Revolution was the dramatic rationalization of measures by the new metric system. The change was extremely unpopular, however, and a metricized version of the traditional unitsthe had to be brought back into use for several decades.
History
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 Magna Carta had 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 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. Some of the differences were large: for example 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
These definitions use the Paris definitions for the coutume of Paris,See :fr:Droit coutumier en France. and definitions for other Ancien régime civil jurisdictions varied, at times quite significantly.
Length The medieval 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 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 around 11 mm (0.56%) 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 metres (about ).
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.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.
+Table of length unitsUnit Relativevalue(pieds) SIvalue(approx.) Imperialvalue(approx.) Notes point 0.188 mm 7.401 thou of a ligne. This unit is usually called the Truchet point in English. Prior to the French Revolution the Fournier point was also in use. It was of a ligne or of the smaller French foot. ligne 2.256 mm 88.81 thou of a pouce. This corresponds to the line, a traditional English unit. pouce 27.07 mm 1.066 in 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 (properly a separate, shorter unit), the , or . toise 6 1.949 m 6.394 ft, or2.131 ydSix pieds du roi. This corresponds to the fathom, a traditional English unit. Unlike the fathom, it was used in both land and sea contexts.The was introduced in 1668 and defined by an iron bar on the Grand Chatelet. This was replaced by the in 1766. Paris perche d'arpent 22 7.146 m 7.815 yd Related to, but not directly corresponding with, the English perch or rod (which is 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 milesThis 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 milesThis league was defined in 1674 as exactly 2000 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 milesThis league is 2200 toises or 60 arpents. It was created in 1737. lieue de 25 au degré ~13 692 4.448 km 2.764 milesLinked 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 2282 toises. lieue tarifaire 14 400 4.678 km 2.907 milesThis league is 2400 toises. It was created in 1737. North America perche du roi 18 5.847 m 6.394 ydThis perch was used in Quebec and Louisiana arpent (du roi) 180 58.47 m 63.94 ydTen perches du roi. Local perche ordinaire 20 6.497 m 7.105 ydThis perch was used locally. arpent (ordinaire) 200 64.97 m 71.05 ydTen perches ordinaires.
The French typographic point, the Didot point, was of a French inch, i.e. two royal points. The French pica, called Cicéro, measured 12 Didot points or 12 × 0.376 = .
Area
+Table of area units Unit Relativevalue(pieds carrés) SIvalue Imperialvalue Notes pied carré 1 ~1055 cm2 ~1.136 sq ftThe French square foot toise carrée 36 ~3.799 m2 ~40.889 sq ft, or~4.543 sq ydThe French square fathom Paris perche d'arpent carrée 484 ~51.07 m2 ~61.08 sq ydThis 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 ydA square 5 perches on each side, or one quarter of an acre. acre, orarpent carré 48 400 ~5107 m2 ~6108 sq yd, or~1.262 acresThe 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.) North America perche du roi carrée 324 ~34.19 m2 ~40.89 sq ydThis square perch was used in Quebec and Louisiana. It is a square 18 pieds du roi on each side. vergée (du roi) 8100 ~854.7 m2 ~1022 sq ydA square 5 perches du roi on each side. acre (du roi), orarpent carré 32 400 ~3419 m2 ~4089 sq yd, or~0.8448 acresA 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. Local perche (ordinaire) carrée 400 ~42.21 m2 ~50.48 sq ydThis square perch was used locally. It is a square 20 pieds du roi on each side. vergée (ordinaire) 10 000 ~1055 m2 ~1262 sq ydA square 5 perches ordinaires on each side. acre (ordinaire), orarpent carré 40 000 ~4221 m2 ~5048 sq yd, or~1.043 acresA square 10 perches ordinaires on each side.
Volume – liquid measures
+Table of (liquid) volume units Unit Relativevalue(pintes) SIvalueU.S.valueImperialvalue Notes roquille ~29.75 mlOne quarter of a poisson. poisson ~119 mlA measure equal to a half a demiard. There were different sizes based on the commodity measured: poisson de vin (wine), poisson de eau de vie (brandy), or poisson de lait (milk).Dictionnaire de l'Academie Francais (8th edition) demiard ~238 ml ~0.5 pintdemi in French means "half": in this case, half a chopine, and – coincidentally – also approximately half a US pint [237 ml]. chopine ~476.1 ml ~1 pint ~0.84 pint pinte 1 ~952.1 ml ~2.01 pint ~1.68 pintAlthough 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 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 a velte was a measuring stick that was inserted into a cask or barrel to determine its depth. quartaut 72 ~68.55 L 9 veltes, or two cubic pieds du roi. feuillette 144 ~137.1 L muid 288 ~274.2 LEight cubic pieds du roi. cubic pouce cube ~19.84 mlThe French cubic inch. pied cube 36 ~34.28 LThe French cubic foot. In ancient times, a cubic foot was also known as an amphora when measuring liquid volume.
Volume – dry measures
+Table of (dry) volume units Unit Relativevalue(boisseaux) SIvalue Imperialvalue U.S.value Notes litron ~ of a quart. The litre is etymologically related to this unit. quart ~ of a boisseau. boisseau 1 ~Although etymologically related to the English unit bushel, the French bushel is about one third the size. A boisseau was defined as of a cubic pied du roi. minot 3 ~ mine 6 ~ setier 12 ~ muid 144 ~ cubic pouce cube ~19.84 cm3 ~The French cubic inch. pied cube ~34.28 dm3 ~The French cubic foot. Exactly 2.7 boisseaux.
Weight + The Parisian equivalents (in livres) of 100 local livres in various towns in 1768(approximations per source) Abbeville 93–94 Avignon 83 Beaucare 95 Bordeaux 100 Bourg-en-Bresse 96 Dunkirk 87 Lille 87–88 Lyon 87 Marseilles 81 Montepellier 83 Nancy 94–95 Nantes 101–102 La Rochelle 101–102 Rouen (poids de vicomté) 103 Strasbourg (petit poids) 96 Toulouse 84 + Differences between the nominal and actual weights (in marcs moyens) in the parts of the pile de Charlemagne as measured by Jean-Charles de Borda Nominal(marcs) Error in actual(grains) 20 +1.4 14 +4.5 8 -0.4 4 -2.1 2 -1.0 1 (creux) -0.7 1 (plein) -1.7 Charlemagne's system had 12 onces (ounces) to the livre (pound). Between 1076 and 1093 Philip I (1052–1108) instituted a system of poids de marc (mark weight) used for minting coin, with 8 onces to a marc.
Jean II (1319–1364) 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 an Old French word (ca. 1190, Anglo-Norman dialect) that referred to Scottish coin (sterling, or ″denier″). As references cited later on this page show, its application changed over time in accordance with the changing historical context, though it is not current in 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 (cf. English hundredweight).