Ligne

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

One twelfth of a pouce (about 2.256 mm). The old French line; watchmakers still quote movement sizes in lignes.

1 ligne = 0.002255829062 meters (approximately).

About the ligne

Ligne is simply the French word for line, and the unit sat at the bottom of the Paris measuring ladder: twelve lignes made one pouce, and 144 made one pied du roi. Using the figure adopted in the 1799 metric law, in which one metre equals 443.296 lignes, a ligne comes to about 2.2558 millimetres.

Tailors, cabinetmakers and instrument makers of the Ancien Régime used it for fine dimensions that an inch was too coarse to express. A British line of one twelfth of an English inch also existed until 1824, so the two were similar in spirit but not identical, since the French inch was the longer one.

The unit outlived the monarchy in a few trades. French and Swiss watchmakers still describe the size of a movement or case in lignes, written with a triple prime mark, and milliners measure hat ribbon in it. The button trade uses a different ligne of one fortieth of an inch, about 0.635 millimetres, so the context always has to be checked.

Sources: Wikipedia: Ligne (unit); Wikipedia: Pied du roi; Wikipedia: Traditional French units of measurement

Ligne conversion chart

1 ligne expressed in every other length unit:

More French (Ancien Régime) units

• pouce (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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