Old French Units

200px, Woodcut dated 1800 illustrating the new decimal units which became the legal norm across all France on 4 November 1800

The traditional French units of measurement prior to metrification 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 variously localities introduced their own variants. Some of Charlemagne's units, such as the king's foot (french: pied du Roi) 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 as 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 the 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, 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 (0.55%) 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 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.Weights and Measures Act, Schedule III
/ref> This makes the Quebec ''pied'' very slightly smaller (about 4 parts in one million) than the ''pied'' used in France.

* 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 inch.

Area

Volume – liquid measures

Volume – dry measures

Mass

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 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'' (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 33 ''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 (including the 20 marc outer container); 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 230 400 ''grains'' (the number of grains in 50 ''marcs'').
Louis Lefèvre‑Gineau initially determined that the metric mass of the whole ''pile'' was 12.227 947 5 kg, later corrected to 12.2376 kg, thereby making (by division and rounded to three decimal places) a ''marc'' 244.753 g, a ''livre esterlin'' 367.129 g, and a ''livre actuelle'' 489.506 g.
Hence further the (Parisian) ''once'' was 30.594 g, the ''gros''/''drachme'' was 3.824 g, the ''denier''/''scruple'' was 1.274 g, and the ''grain'' was 0.053 g.

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 399.6 g, the Montpelier one 394.9 g, the Toulon one 465.5 g, and the Toulouse one 413.2 g; with all of the fractional subdivisions having different values accordingly.
The Limoges ''marc'' was 240.929 g, the Tours one 237.869 g, and the Troyes one 250.050 g.

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 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.

See also

* International System of Units
* Jean-Antoine Chaptal
* Mansus
* Mesures usuelles
* Réaumur scale
* Systems of measurement
* Weights and measures

References

Sources

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Further reading

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Systems of units
Science and technology in France