What it is
The ligne (often written L) is the button-trade unit for diameter. 40 ligne = 1 inch exactly. Not the old Paris typographic line, not Chinese cun, not Japanese sun.
How to use
Divide the L number on a button card or pattern by 40 to get inches. 24 ligne = 0.6 in. Reverse: inches × 40. The converter above uses this exact factor.
in = ligne × 0.025
Example: 1 ligne = 0.025 in
Common uses
Shirt buttons about 16-18 ligne (0.4-0.45 in); suit front buttons often 24-28 ligne (0.6-0.7 in); coats 32-36 ligne (0.8-0.9 in). A 3/4-inch button is 30 ligne.
Conversion tips
40 ligne = 1 inch exactly. 16L=0.4 in, 18L=0.45 in, 24L=0.6 in, 30L=0.75 in. Do not mix ligne with denier.