Foot (unit)

A foot (plural: feet; abbreviation or symbol: ft or ′ (the prime symbol) is a unit of length defined as being 0.3048 m exactly and used in the imperial system of units and United States customary units. It is subdivided into 12 inches.

Historically the foot was also used in a number of other systems of units including those from Ancient Greece, Ancient Rome, England, Scotland and many Continental European countries. However, the size of the measure varied from country to country and in some cases from city to city, mostly from about 250mm to 335 mm, The foot measure was also subdivided into 12 inches. Confusion between the British foot (304.8mm) and the French foot (322.5mm or 329.8mm) led to the myth of Napoleon's shortness.

The United States is the only industrialized nation that uses the international foot (a customary unit of length) and the survey foot in preference to the meter in its commercial, engineering and standards activities. The foot is still legally recognized as an alternative expression of length in Canada, officially defined as a unit derived from the metric metre and still commonly used in the United Kingdom, although both have partially metricated their units of measurement. The measurement of altitude in the aviation industry is one of the few areas where the foot is widely used outside the English-speaking world.