Feet (unit of length)
A foot is a non-SI unit of distance or length. The popular belief is that original standard was the length of a man's foot. However, average foot length is about 240 mm (9.4 in) for current Europeans. So the explanation must be slightly more involved. There are twelve inches in one foot and three feet in one yard.
The standardization of weights and measures has left several different standardized foot measures.
The most commonly used foot today is the imperial foot, which is defined to be exactly 0.3048 metres. This unit is sometimes denoted with a prime (e.g. 30′ means 30 feet), often approximated by an apostrophe. Similarly, inches can be denoted by a double prime (often approximated by a quotation mark), so 6′2″ means 6 feet 2 inches.
The foot as a measure was used in almost all cultures. The first known standard foot measure was from Sumeria, where a definition is given in a statue of Gudea of Lagash from around 2575 BC.
The imperial foot was adapted from an Egyptian measure by the Greeks, with a subsequent larger foot being adopted by the Romans.
In addition to the current standard imperial foot, there is also a slightly different U.S. survey foot, used only by the U.S. Coast and Geodetic Survey, defined as exactly 12 U.S. survey inches, approximately 30.48006 cm.
See also
