Inch
The inch is a unit of length equal to one twelfth of a foot, or exactly 25.4 millimeters. It is abbreviated in or marked with a double prime symbol (").
The inch was set at exactly 25.4 millimeters by the same 1959 agreement that fixed the international foot. In construction it is divided into fractions such as halves, quarters, eighths and sixteenths rather than decimals.
Wall thicknesses, window and door sizes, and lumber dimensions are usually given in inches.
Leftover inches matter in area calculations. A room that is 11'9" by 13'4" is about 11.75 by 13.33 feet, or roughly 157 square feet, not the 143 you get by dropping the inches.
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