Pouce

French (Ancien Régime)Historical unit (no longer in standard use)

The old French inch, about 2.707 cm; slightly longer than the English inch.

1 pouce = 0.02706994875 meters (approximately).

About the pouce

Pouce means thumb in French, the same body-part logic found in many inch-like units. In the royal system it was one twelfth of the pied du roi, which gives about 27.07 millimetres, or roughly 1.066 English inches. Each pouce was in turn divided into twelve lignes.

Craftsmen, surveyors and builders across France quoted lengths in pieds, pouces and lignes until the metric reforms of the 1790s, and the pouce was the natural unit for small dimensions. Because the French inch was slightly longer than the English one, converting between the two traditions always needs the exact ratio and not a rough equivalence.

The pouce shared the history of the foot it came from. Its size depended on the royal standard, which was an iron toise bar kept in Paris, and that bar was replaced after it was found deformed in 1668. Under the metric law of 1799 it was fixed in relation to the metre, and the same ratio is quoted today.

Sources: Wikipedia: Pied du roi; Wikipedia: Traditional French units of measurement; Wikipedia: Toise

Pouce conversion chart

1 pouce expressed in every other length unit:

More French (Ancien Régime) units

• ligne (length)
• pied du roi (length)
• toise (length)
• lieue (Paris league) (length)
• arpent (North American) (area)
• degree Réaumur (temperature)
• degree Delisle (temperature)
• poncelet (power)
• pièze (pressure)
• sthène (force)

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