【How-to】How much is one inch in cm

The unit derives from the Old English ince, or ynce, which in turn came from the Latin unit uncia, which was “one-twelfth” of a Roman foot, or pes. (The Latin word uncia was the source of the name of another English unit, the ounce.) … Since 1959 the inch has been defined officially as 2.54 cm.