An uncia (plural: unciae) is an ancient Roman unit of length that roughly corresponds to an inch. One uncia is 0.97 inches or 24.6 millimeters. There are twelve uncia in one pes.
The word uncia was Latin for a unit equal to 1/12 of another unit. The words inch (1/12 of a foot) and ounce (originally 1/12 of a pound and still 1/12 of a troy pound) are derived from the word uncia.