<Tr> <Th> imperial / US units </Th> <Td> 1 / 3 yd 12 in </Td> </Tr> <Tr> <Th> metric (SI) units </Th> <Td> 0.3048 m </Td> </Tr> <P> The foot (pl . feet; abbreviation: ft; symbol: ′, the prime symbol) is a unit of length in the imperial and US customary systems of measurement . Since 1959, both units have been defined by international agreement as equivalent to 0.3048 meters exactly . In both systems, the foot comprises 12 inches and three feet compose a yard . </P> <P> Historically the "foot" was a part of many local systems of units, including the Greek, Roman, Chinese, French, and English systems . It varied in length from country to country, from city to city, and sometimes from trade to trade . Its length was usually between 250 mm and 335 mm and was generally, but not always, subdivided into 12 inches or 16 digits . </P>

One foot is equal to how many inches