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The foot (standard symbol: ft) [1] [2] is a unit of length in the British imperial and United States customary systems of measurement. The prime symbol, ′, is commonly used to represent the foot. [3] In both customary and imperial units, one foot comprises 12 inches, and one yard comprises three feet.
The basic unit of length in the imperial and U.S. customary systems is the yard, defined as exactly 0.9144 m by international treaty in 1959. [2] [5] Common imperial units and U.S. customary units of length include: [6] thou or mil (1 ⁄ 1000 of an inch) inch (25.4 mm) foot (12 inches, 0.3048 m) yard (3 feet, 0.9144 m)
In antiquity, systems of measurement were defined locally: the different units might be defined independently according to the length of a king's thumb or the size of his foot, the length of stride, the length of arm, or maybe the weight of water in a keg of specific size, perhaps itself defined in hands and knuckles.
The modern Brannock device takes three measurements of each foot: Foot length the length from heel to the tip of the longest toe (in increments of barleycorns) Arch length the length from heel to the inside of the ball of the foot, or medial metatarsophalangeal joint Width the width of the foot perpendicular to the length
Metric units are units based on the metre, gram or second and decimal (power of ten) multiples or sub-multiples of these. According to Schadow and McDonald, [1] metric units, in general, are those units "defined 'in the spirit' of the metric system, that emerged in late 18th century France and was rapidly adopted by scientists and engineers.
The agricultural foot was reduced to 10 ⁄ 11 of its former size, causing the rod, pole or perch to become 16 + 1 ⁄ 2 (rather than the older 15) agricultural feet. The furlong and the acre, once it became a measure of the size of a piece of land rather than its value, remained relatively unchanged. In the last thousand years, three principal ...
This differs from many older systems in which the ratio of different units varied. For example, 12 inches is one foot, but the larger unit in the same system, the mile is not a power of 12 feet. It is 5,280 feet – which is hard to remember for many. [5]: 17
For measuring length, the U.S. customary system uses the inch, foot, yard, and mile, which are the only four customary length measurements in everyday use.From 1893, the foot was legally defined as exactly 1200 ⁄ 3937 m (approximately 0.304 8006 m). [13]