A digit (lat. finger), when used as a unit of length, is usually a sixteenth of a foot, i.e. 3/4″ or 1.905 cm (for the international inch). The width of an adult human male finger tip is indeed about 2 centimetres. In English this unit has mostly fallen out of use, as do others based on the human arm: finger (7/6 digit), palm (4 digits), hand (16/3 digits), shaftment (8 digits), span (12 digits), cubit (24 digits) and ell (60 digits).

It is in general equal to the nail, although that unit can also be used differently.