The ligne (pronounced [liɲ] ), or line or Paris line,[1] is a historic unit of length used in France and elsewhere prior to the adoption of the metric system in the late 18th century, and used in various sciences after that time.[2][3] The loi du 19 frimaire an VIII (Law of 10 December 1799) states that one metre is equal to exactly 443.296 French lines.[4]

Unit systemFrench
Unit oflength
1 ligne in ...... is equal to ...
   French units   12 Truchet point
1/12 pouce
   metric (SI) units   2.2558 mm
   imperial/US units   0.08881 in

It is vestigially retained today by French and Swiss watchmakers to measure the size of watch movements,[5] in button making, and in ribbon manufacture.

Current use


The ligne is still used by French and Swiss watchmakers

There are 12 lignes to one French inch (pouce). The standardized conversion for a ligne is 2.2558291 mm (1 mm = 0.443296 ligne),[4] and it is abbreviated with the letter L or represented by the triple prime, . One ligne is the equivalent of 0.0888 international inch.

This is comparable in size to the British measurement called "line" (one-twelfth of an English inch), used prior to 1824.[6] (The French inch at that time was slightly larger than the English one, but the system of 12 inches to a foot and 12 lines to an inch was the same in both cases.)


In the 18th century German button makers began to use the term ligne to measure the diameter of buttons. The consensus definition was that a ligne was the measurement of a round wick, folded flat. In this sense it measures 140 of an inch, but not exactly, for there were several inches in the kingdoms and petty states of Germany at that time.

Such a measurement became the American measurement called "line", being one-fortieth of the US-customary inch, used to measure buttons, probably introduced by German immigrants. [7][better source needed] It remains in US use today for buttons and snaps.[citation needed]


Ligne is used in measuring the width of ribbons in men's hat bands,[8] at 11.26 per inch.[9]

See also



    1. Gates, E.J. (1915). "The Determination of the Limens of Single and Dual Impression by the Method of Constant Stimuli". The American Journal of Psychology. 26 (1): 152–157. doi:10.2307/1412884. JSTOR 1412884.
    2. Stearn, W.T. (1992). Botanical Latin: History, grammar, syntax, terminology and vocabulary, Fourth edition. David and Charles.
    3. Neumann, F. (January 1863). "IX. Experiments on the calorific conductibility of solids". Philosophical Magazine. 4. 25 (165): 63–65. doi:10.1080/14786446308643418.
    4. Suzanne Débarbat. "Fixation de la longueur définitive du mètre" [Establishing the definitive metre] (in French). Ministère de la culture et de la communication (French ministry of culture and communications). Retrieved 2011-03-01.
    5. Foire aux questions sur l'horlogerie et les montres [Frequently asked questions about watches and clocks] (in French),, retrieved 2010-06-30, Chaque ligne équivaut à 2,2558 mm, arrondis à 2,26 mm pour calculer plus rapidement. [Each line equals 2.2558 mm, rounded to 2.26 mm for faster calculation.].
    6. Oxford English Dictionary