Foot (unit of length)

A foot (plural: feet; symbol or abbreviation: ft or, sometimes, ′ - a prime) is the name of a unit of length, in a number of different systems, including English units, Imperial units, and United States customary units. Its size can vary from system to system, but in each is around a quarter to a third of a meter. The most commonly used foot today is the international foot. There are 3 feet in a yard and 12 inches in a foot.

The foot is a common and popular unit of measurement in the United States, the United Kingdom and Canada. In the US and the UK, personal heights are expressed in feet and inches by people of all ages. In Canada, the trend has been shifitng towards metres, as shown on a person's driver's license. The foot is often used to measure distance.

International foot

In 1958 the United States and countries of the Commonwealth of Nations defined the length of the international yard to be 0.9144 metres. Consequently, the international foot is defined to be equal to 0.3048 metres (equivalent to 30.48 centimetres).

The international standard symbol for a foot is "ft" (see ISO 31-1, Annex A). In some cases, the foot is denoted by a prime, which is often approximated by an apostrophe, and the inch by a double prime. For example, 6 feet 2 inches is denoted by 6′2″. This use can cause confusion, because the prime and double prime are also international standard symbols for arcminutes and arcseconds.

United States survey foot

The United States survey foot is defined as 1200/3937 metres. It is used only in connection with surveys by the U.S. Coast and Geodetic Survey. It is 610 nm greater than the international foot. ^*

Historical origin

The foot as a measure was used in almost all cultures and was usually divided into 12, sometimes 10 inches / thumbs or into 16 fingers / digits. 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. Some metrologists speculate that the imperial foot was adapted from an Egyptian measure by the Greeks, with a subsequent larger foot being adopted by the Romans.

Etymology

The popular belief is that original standard was the length of a man’s foot.

Some believe that the original measurement of the English foot was from King Henry I, who had a foot 12 inches long; he wished to standardise the unit of measurement in England. However this is unlikely, because there are records of the word being used approximately 70 years before his birth (Laws Æthelstan). The average foot length is about 9.4 inches (240 mm) for current Europeans. Approximately 99.6% of 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.

External links

http://www.knowledgedoor.com/1/Library_of_Units_and_Constants/Group_Index/foot_group.htm
Metric unit conversion

Units of length | Imperial units | Customary units in the United States | Human-based units of measure

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International foot

United States survey foot

Historical origin

Etymology

See also

External links