French units of measurement

French system

In France, before the decimalised SI 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.

In Paris, the redefinition in terms of metric units made 1 decimal meter exactly 443.296 French lines = 3 French feet, 0 French inch and 11.296 French lines.

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. Thus a square arpent was 5299296.0804 in² or about 36,801 ft² or 0.8448 acre.

Modern metrologists now consider that the historical ratio between the English and the French foot was indeed 16 to 15.
So, the French foot should normally measure 12.8 English inches, i.e. about 0.086 % or 0.28 mm more than the Québécois value.

Length

French unit (English name)	French name	Ratio	Equivalence in PS pica	Equivalence in SI metre
one point	point	1 / 1728	0 .533	0. 188 mm
one line	ligne	1 / 144	6 .400	2. 256 mm
one inch	pouce	1 / 12	76 .800	2. 707 cm
one Royal foot	pied du Roi	1	921 .600	32. 484 cm
one fathom	toise	6	5,529 .600	1. 949 m
one perch	perche	18	16,588 .800	5. 847 m
one league	lieue	12,000	11,059 ,200	3. 898 km
The decimal meter of 1799 was defined 443.296 Royal lines. Since the French foot is exactly 9,000 / 27,706 SI meters. However, the "Pied du Roi" – as half-a-Hashimi cubit – is sixteen fifteenth of the English foot, since this one is four 7th of the well-known Ptolemaic cubit. The difference of about 0.086 % is owed to mutually not-adjusted standards.

• Next to this Royal main system, other ratios has been used. For example the surveying "perche des Eaux et Forêts" of 22 Royal feet and the "ordinary perch" of 20 Pied du Roi. From there other leagues were deduced.
• The French typographic point, the Didot point, was 1/72 French inches, i.e. two Royal points. The French pica, called "Cicéro", measured 12 points Didot.

Area

French unit	Ratio	pied carré	in square meter
one pied carré	1 / 484	1	0 .105 5
one toise carrée	9 / 121	36	3 .798 7
one perche carrée	1	484	51 .072 0
one old are	2	968	102 .144 0
one vergée	25	121 x 100	1 276 .799 6
one acre	100	484 x 100	5 107 .198 3

Volume

Liquid measures

French unit	Ratio	Cubic pouces	Equivalence
one roquille	1 / 16	1½	29. 755 mL
one posson	1 / 4	6	119. 018 mL
one demiard	1 / 2	12	238. 036 mL
one chopine	1	24	476. 073 mL
one pinte	2	48	952. 146 mL
one quade	4	96	1. 904 L
one velte	16	384	7. 617 L
one quartaut	144	2 x 1728	68. 555 L
one feuillette	288	4 x 1728	137. 109 L
one muid	576	8 x 1728	274. 218 L
The muid is defined as eight amphoras, i.e. 8 cubic pieds-du-Roi. As there are 4096 cubic Roman digits in the Roman amphora quadrantal, there are exactly 1728 French cubic pouces-du-Roi in the French standard jar.

Dry measures

French unit	Ratio	Cubic pouces	Equivalence
one litron	1 / 16	40	79. 345 cL
one quart	1 / 4	160	3. 174 L
one boisseau	1	640	12. 695 L
one minot	3	1 920	38. 086 L
one mine	6	3 840	76. 172 L
one setier	12	7 680	152. 343 L
one muid	144	92 160	18. 281 hL

Weight

French unit	Ratio (ounce)	Ratio (pound)	Half-a-grain (multiples)	Equivalence (rounded)
[half-a-grain]	1 / 1152	1/ (384x48)	1	26, 557 4 mg
one grain	1 / 576	1/ (384x24)	2	53, 114 8 mg
one denier	1 / 24	1 / 384	48	1, 274 8 g
one gros	1 / 8	1 / 128	144	3, 824 3 g
one once	1	1 / 16	1 x 1152	30, 594 1 g
one marc	8	1 / 2	8 x 1152	244, 752 9 g
one livre	16	1	16 x 1152	489, 505 8 g
one quintal	1600	100	1600 x 1152	48, 950 6 kg
The livre (pound) was defined 1/70 French talent, i.e. the foot cube filled with water.
le talent	1120	70	1120 x 1152	34, 265 4 kg

See also

• Weights and measures
• Historical weights and measures
• Mesures usuelles
• SI