Inch

An inch (plural: inches; abbreviation or symbol: in or ″ – a double prime) is a unit of length in a number of systems of measurement, including the imperial and United States customary systems. One imperial or US customary inch is defined as 1⁄₁₂ of a foot and is therefore 1⁄₃₆ of a yard. Traditional standards for the exact length of an inch have varied, but it is now defined to be exactly 25.4 mm.