A foot (plural: feet) is a non-SI unit of distance or length, measuring around a third of a meter. There are twelve inches in one foot and three feet in one yard. The international standard symbol for feet is ft (see ISO 31-1, Annex A).
The standardization of weights and measures has left several different standard foot measures. The most commonly used foot today is the English foot, used in the United Kingdom and the United States and elsewhere, which is defined to be exactly 0.3048 meters. 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.
In addition to the current standard international foot, there is also a slightly different U.S. survey foot, used only in connection with surveys by the U.S. Coast and Geodetic Survey, it is defined as exactly 1200/3937 m (610 nm greater than 0.3048 m).
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.
The popular belief is that original standard was the length of a man's foot. The original measurement was from King Henry I, who had a foot 12 inches long; he wished to standardise the unit of measurement in England. The average foot length is about 9.4 inches (240 mm) for current Europeans. Approximately 996 out of 1000 British men have a foot that is less than 12 inches long. A plausible explanation for the missing inches is that the measure did not refer to a naked foot, but to the length of footwear. This is consistent with the measure being convenient for practical purposes such as on building sites etc. People almost always pace out lengths whilst wearing shoes or boots, rather than removing them and pacing barefoot.
Zie voor meer --> internet