French units of measurement

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[edit] 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 metre 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 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.

[edit] Length

French unit
(English name)		 French name Ratio Equivalence
in DTP points		 Equivalence
in metres
one Truchet point point 1/ 1728
0 .53
0. 188 mm
one line ligne 1/ 144
6 .4
2. 256 mm
one inch pouce 1/ 12
76 .8
2. 707 cm
one royal foot pied du roi 1
921 .6
32. 484 cm
one fathom toise 6
5 529 .6
1. 949 m
one perch perche 18 
16 588 .8
5. 847 m
one league lieue 12 000 
11,059  200
3. 898 km
The decimal metre of 1799 was defined 443.296 royal lines.
Thus:  The French foot is exactly  9 000 / 27 706 metre. 
Historically, 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.
one surveying perch perche d'arpent 22
20 275 .2
7. 146 m
one arpent length longueur d'arpent 220
202 752
71. 465 m
The surveying perch in France generally measured 22 royal feet.
The arpent length was always 10 perches, thus mostly 220 royal feet.
In Quebec and Louisiana land surveyers used the royal perch of 18 French feet.

[edit] Area

French unit Ratio pied carré     in m²
one pied carré 1  / 484 1
0 .105 5
one toise carrée 9  / 121 36
3 .798 7
one royal square perch 81 / 121 18² = 324
34 .188 7
one ordinary square perch 100 / 121   20² = 400
42 .208 3
one square perch 1 22² = 484
51 .072 0
one vergée 25 110² = 12100
1 276 .799 6
one acre 100  220² = 48400
5 107 .198 3

The square perch means the main square perch in ancient French surveying. The French surveyor perch measured 22 royal feet.
Locally only, the acre could also measure 40000 French square feet, i.e. 100 ordinary square perches of 20 royal feet per perch.
Especially in Quebec and Louisiana the acre was 32400 French square feet, 100 royal perches, i.e. about 34.188 683 are.
Thus, this particular French-American acre is also about 0.6694 French standard acre and about 0.8448 English acre.
The term "square arpent" is synonym to the French acre. It measured generally 48400 French square feet. Anyway, a vergée is always the fourth of its respectiv acre.

[edit] Volume

[edit] Liquid measures

French unit Ratio Cubic pouces Equivalence
one cubic pouce 1/ 48 1
19. 836 mL
one roquille 1/ 32 1½
29. 755 mL
one posson 1/ 8 6
119. 018 mL
one demiard 1/ 4 12
238. 036 mL
one chopine 1/ 2 24
476. 073 mL
one pinte 1 48
952. 146 mL
one quade 2 96
1. 904 L
one velte 8 384
7. 617 L
one cubic pied 36 1 x 1728
34. 277 L
one quartaut 72 2 x 1728
68. 555 L
one feuillette 144  4 x 1728
137. 109 L
one muid 288  8 x 1728
274. 218 L
The muid is defined as eight cubic pieds-du-roi, i.e. 8 x 1728 cubic pouces.

[edit] Dry measures

   French unit
Ratio
(boisseau)
Ratio
(cubic pied)
10 cubic
pouces
Equivalence
one cubic pouce
1/ 640
1 / 1728  
  0.1
19. 836 mL
one litron
1/ 16
5 / 216  
4
79. 345 cL
one quart
1/ 4
5 / 54  
16
3. 174 L
one boisseau
1
10 / 27  
64
12. 695 L
one minot
3
10 / 9  
192
38. 086 L
one mine
6
20 / 9  
384
76. 172 L
one setier
12
40 / 9  
768
152. 343 L
one muid
144 
480 / 9  
9216
18. 281 hL
There are twenty-seven boisseaux exactly in ten cubic pieds-du-roi.
Remark:  The French use of the term boisseau differs with the universal use.
Since the dry volume measure bushel is normally identical to one cubic foot.
The french "minot" corresponds to one cubic pied-du-roi and plus its ninth.
one cubic pied
27 / 10
1
  172.8
34. 277 L

[edit] Weight

Poids de marc, mid 14th – late 18th century

  French unit Ratio
(ounce)		 Ratio
(pound)		 Ratio
(prime)		 Equivalence
(rounded)
  one prime
1/ (576x24) 1/ (384x576)
  1
2. 213 1 mg
  one grain
1/ 576 1/ (384x24)
  24
53. 114 8 mg
  one denier
1/ 24 1/ 384
  576
1. 274 8 g
  one gros
1/ 8 1/ 128
  1728
3. 824 3 g
  one once
1 1/ 16
8 x 1728
30. 594 1 g
  one marc
8 1/ 2
64 x 1728
244. 752 9 g
  one livre
16  1
128 x 1728
489. 505 8 g
  one quintal
1600  100
12800 x 1728
48. 950 6 kg
The livre was defined 1/ 70 French talent,  i.e. the cubic foot filled with water.
  one talent
1120  70
8960 x 1728
34. 265 4 kg
Bullion dealers also used the special units :   estelin, maille and felin.
  one estelin
1/ 20  1/  320
3456 /   5
1. 529 7 g
  one maille
1/ 40  1/  640
1728 /   5
0. 764 9 g
  one felin
1/ 80  1/ 1280
864 /   5
0. 382 4 g

[edit] See also

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