foot, in measurement, any of numerous ancient, medieval, and modern linear measures (commonly 25 to 34 cm) based on the length of the human foot and used exclusively in English-speaking countries, where it generally consists of 12 inches or one-third yard. In most countries and in all scientific applications, the foot, with its multiples and subdivisions, has been superseded by the metre, the basic linear unit in the metric system. In the United States the definition of the foot as exactly 30.48 cm took effect in 1959.