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US Customary System of Units

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: ''This article describes US Customary units. For instructions on how to convert between US Customary and metric units, see [[English and Metric Units]].''
The '''United States Customary System of Units''' (or more commonly within the [[United States]] - '''standard units'''), or, in the [[United Kingdom]], '''Imperial units''' are units of measurement. It is one of two primary systems of measurement. The other, the [[metric system]], enjoys widespread use outside of the United States. Only two countries have not officially adopted the metric system - [[Liberia]] and [[Burma]].<ref>{{cite web|url=|title=FAQ: Frequently Asked Questions about the metric system|format=HTML|language=English|work=U.S. Metric Association|accessdate=2007-09-03}}</ref>
As a matter of law, all US Customary units are defined in terms of their [[Metric system|metric]] counterparts.
== Length ==
The units of length in the US Customary system are the inch, the foot, the yard, and the mile.
:12 in = 1 ft
:3 ft = 1 yd
:5,280 ft = 1 mi
=== Inch ===
* The ''fathom'' is the length of a rope held between two outstretched arms. It is defined as six feet. It is used as a unit of depth at sea by British mariners, but the usual unit of depth at sea in the USA is the foot.
* The ''rod'' is the length of a queue of sixteen persons. By convention, the rod is defined as five and one-half yards, or sixteen and one-half feet. 320 rods would therefore make a mile. The rod is rarely if ever used as a measure nowadays.
* The ''furlong'' is one-eighth of a mile, or 40 rods. It is close in length to the Roman stadium, which was one-eighth of a Roman mile.It is used in [[horse racing]]
* The ''chain'', one-eightieth of a mile or 66 feet. It is used in land measure and on the railways. Importantly, the distance between the sets of stumps on a [[cricket]] pitch is 1 chain.
One ''acre'' is 160 square ''rods''. 640 acres make a square mile.
== Weight and mass ==
The US Customary system uses [[Avoirdupois]] weight. Effective July 1, 1959, the US Customary avoirdupois pound has been set equal to the international pound, and this in turn is based on a prototype pound in the British Exchequer.<ref name=pounddef>[ Pound avoirdupois] at</ref> All other units of weight derive from this prototype. To be specific:
=== Stone ===
The stone, a unit of 8 &nbsp;lb, is very commonly used in the UK as a measure of weight, especially of people and animals. It is common, for example, for a British person to express his or her weight as ''9 stone 8 pounds'' (written 9st 4lb4&nbsp;lb), meaning 130 &nbsp;lb or approximately 59kg59&nbsp;kg.
=== Hundredweight ===
Originally the English system defined the ''hundredweight'' (abbreviated cwt) as one hundred pounds. This is slightly heavier than an ancient [[talent]]. In the UK, 1 hundredweight (cwt) is now defined as 8 stone, i.e. 112 &nbsp;lb; the hundredweight is still quite widely used as a measure of weight in the UK.
=== Ton ===
One US (or "short") ton is 2,000 pounds. An Imperial ("long") ton is 20 hundredweight or 160 stone or 2,240 pounds. The latter is being replaced by the ''metric ton'' (tonne) of 1,000 &nbsp;kg, or about 2,207 pounds.
== Mass ==
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