Mesures usuelles (French pronunciation:[məzyʁyzɥɛl],customary measures) were aFrench system of measurement introduced byFrench EmperorNapoleon I in 1812 to act as compromise between themetric system andtraditional measurements. The system was restricted to use in the retail industry and continued in use until 1840, when the laws of measurement from 1795 and 1799 were reinstituted.^[1]

In the five years immediately before theFrench First Republic introduced themetric system, every effort was made to make the citizens aware of the upcoming changes and to prepare them for it.^[2] The administration distributed tens of thousands of educational pamphlets, private enterprise produced educational games, guides,almanacs, and conversion aids, and metre standards were built into the walls of prominent buildings aroundParis.^[2] The introduction was phased by district over the next few years, with Paris being the first district to change. The government also realised that the people would need metre rulers, but they had only provided 25,000 of the 500,000 rulers needed in Paris as late as one month after the metre became the sole legal unit of measure.^[2] To compensate, the government introduced incentives for the mass-production of rulers. Paris police reported widespread flouting of the requirement for merchants to use only the metric system.^[2] Where the new system was in use, it was abused, with shopkeepers taking the opportunity to round prices up and to give smaller measures.^[2]

Napoleon I, the French Emperor, disliked the inconvenience of surrendering the highfactorability of traditional measures in the name ofdecimalisation, and recognised the difficulty of getting it accepted by the populace.^[3] Under thedécret impérial du 12 février 1812 (imperial decree of 12 February 1812), he introduced a new system of measurement, themesures usuelles or "customary measures", for use in small retail businesses. However, all government, legal, and similar works still had to use the metric system and the metric system continued to be taught at all levels of education.^[4][5]

Theprototypes of the metric unit, thekilogram and themetre, enabled an immediate standardisation of measurement over the whole country, replacing the varying legal measures in different parts of the country, and even more across the whole ofEurope. The newlivre (known as thelivre métrique) was defined as five hundredgrams, and the newtoise (toise métrique) was defined as two metres. Products could be sold in shops under the old names and with the old relationships to one another, but with metric-based and slightly changed absolute sizes. This series of measurements was calledmesures usuelles.

Napoleon's decree was eventually revoked during the reign of KingLouis Philippe I by theloi du 4 juillet 1837 (law of 4 July 1837), which took effect on 1 January 1840, and reinstated the original metric system. This brought the system ofmesures usuelles to a legal end,^[4] though thelivre remains in some informal use to this day.

The law authorised the following units of measure:^[6]

• Thetoise (fathom) was defined as exactly two metres and was as before divided into 6pieds (or "feet") or 72pouces (inches). Thepouce was divided into 12lignes (or "lines"). Thepied andpouce, at precisely 333.3 mm and 27.7 mm, were about 2.6% larger than the previous Parisian measures and 9% larger than their English counterparts.
• Theaune (ell), used to measure cloth, was defined as 120 centimetres, and divided into thedemi aune (half an ell, or 60 cm) and thetiers aune (third of an ell, or 40 cm). It was 1.3% larger thanl’aune de Paris (118.48 cm) and 5.0% larger than its English counterpart (45 inches; 114.3 cm).^[7]

• Thelitre was subdivided like a Britishquart, intodemis (literally, "halves", being the equivalent of apint of about sixteenfluid ounces),quarts (literally, "fourths", being the equivalent of a cup of about eight fluid ounces),huitièmes (literally, "eighths"), andseizièmes (literally, "sixteenths", of about two fluid ounces).
• Theboisseau, (bushel), was redefined as being an eighth of a hectolitre and with associated measuresdouble-boisseau,demi-boisseau andquart-boisseau (double, half, and quarter bushels respectively). The originalboisseau, like the English bushel, varied depending on thecommodity for which it was used, as well as theregion where it was used.
• Thelivre, (pound), was defined as 500 grams, divided into 16onces, (ounces), eachonce being divided into 8gros. Each gros being thought of as being composed of 72grains, whose name is the same as in English. Hence, the livre was 9216grains.^[8] Thelivre andonce were about 10% larger than their English counterparts, while thegrain was 17% less than its English counterpart.

Themesures usuelles did not include any units of length greater than thetoise - themyriamètre (10 km) remaining in use throughout this period.^[8]

• 1812 introductions
• Systems of units
• Science and technology in France
• Metrication in France
• Obsolete units of measurement
• Napoleon

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