When discussing widths of men's hat ribbons, you will find an old unit of measurement called the French Ligne.  It is sometimes denoted with the triple apostrophe ('''), as in 12''' signifies a "12-ligne hat band.  We have a handy chart for common hat ribbon widths; you can use it to make a rough conversion from lignes to inches.  We only included common ribbon widths.

 4 lignes

3/8 in.
6 lignes 1/2 in.
8 lignes 5/8 in.
9 lignes 3/4 in.
12 lignes

1 in.
16 lignes 1 1/2 in.
19 lignes 1 3/4 in.
22 lignes 2 in.
25 lignes 2 1/4 in.