- ' (the prime symbol)
- (Meaning ten feet can be symbolised as either 10 ft or 10')
- Length / distance
Primarily used as an official unit of measurement in the United States. Canada also recognises the foot as an alternative unit of measurement (to standard metric), and the foot continues to be commonly used in the United Kingdom.
The foot is also used globally to measure altitude in the aviation industry.
The foot is a unit of length used in the imperial and U.S. customary measurement systems, representing 1/3 of a yard, and is subdivided into twelve inches.
In 1959 the international yard and pound agreement (between the United States and countries of the Commonwealth of Nations) defined a yard as being exactly 0.9144 metres, which in turn defined the foot as being exactly 0.3048 metres (304.8 mm).
The foot has been used as a unit of measurement throughout much of recorded history – including in Ancient Greece and the Roman Empire – and the origin of the name is generally accepted to relate to the average size of an adult, male foot (or possibly shoe). Originally divided into sixteen component units, the Romans also divided the foot into twelve uncia – the origin of the modern English term inch.
The foot continued to be used throughout Europe for most of the last two thousand years, although national and regional variations were common. Depending on where (and when) the term foot was used, it could refer to lengths as small as 273 mm or as large as 357 mm. The foot also came to be commonly used in English-speaking countries around the world.
Use of the foot declined as most countries adopted the metric system, starting with France in the late 18th century.
- An association football (soccer) goal is eight feet high by eight yards (24 ft) wide.
- "Six feet under" is a euphemistic phrase for burial in a grave, or more broadly a dead person is sometimes described as being "six feet under".
- "Five Feet High and Rising" (a reference to flood water) was used as a song title by Johnny Cash. De La Soul subsequently titled their 1989 hit hip hop album "3 Feet High and Rising".
In 1995 in the UK the foot, along with the inch, yard and mile, were officially stated as the primary units of measurement for road signs and related measurements of distance and speed. In other contexts metric measurements are now the primary system, although feet are still often used on an informal basis, particularly by people who were born and educated in pre-decimal Britain.
The foot is also used as a base unit in the FPS system, which uses feet, pounds and seconds to derive other units of measurement, such as the poundal (ft•lb-m•s-2) a unit of measurement for force. (The FPS system has been largely replaced by the metric m.k.s. system, based around metres, kilograms and seconds).
- 12 inches = 1 ft
- 3 feet = 1 yd (yard)