Chain (unit)

chain
chain
	The chain is based on the length of Gunter's chain, which is 66 feet (22 yd) long.
General information
Unit system	Imperial/US units
Unit of	length
Symbol	ch
Conversions
1 ch in ...	... is equal to ...
Imperial/US units	22 yd, 66 ft, 100 links
Metric (SI) units	20.1168 m

The chain (abbreviated ch) is a unit of length equal to 66 feet (22 yards), used in both the US customary and Imperial unit systems. It is subdivided into 100 links.^[1]^[2] There are 10 chains in a furlong, and 80 chains in one statute mile.^[2] In metric terms, it is 20.1168 m long.^[2] By extension, chainage (running distance) is the distance along a curved or straight survey line from a fixed commencing point, as given by an odometer.

The chain has been used for several centuries in England and in some other countries influenced by English practice. In the United Kingdom, there were 80 chains to the mile, but until the early nineteenth century the Scottish and Irish customary miles were longer than the statute mile; consequently a Scots chain was about 74 (imperial) feet,^[3] an Irish chain 84 feet. These longer chains became obsolete following the adoption of the imperial system of units in 1824.^[4]

In India, "metric chains" of exactly 20 metres (65.62 feet) are used, along with fractions thereof.^[5]

^ James, Robert C.; James, Glenn (1992). Mathematics Dictionary. New York: Chapman & Hall. p. 453. ISBN 9780412990410.
^ ^a ^b ^c "6 Tables of Interrelation of Units of Measurement". Units of Weight and Measure (United States Customary and Metric): Definitions and Tables of Equivalents (PDF). U.S. Department of Commerce, National Bureau of Standards. 1960. pp. 8–9. (PDF)
^ Smeaton, John (1837). Reports of the Late John Smeaton, F.R.S. (2nd ed.). London: M Taylor. p. 308. Since the foregoing Report [on the best route for the Forth and Clyde Canal] ... was delivered ... , Mr Smeaton has discovered that, notwithstanding the care and pains he took to be correct, he has committed an error, in supposing the Scotch chain, with which the measures of the length of the tract of land were taken, to consist of seventy feet each, whereas, in reality, it consists of seventy-four
^ William John Macquorn Rankine (1863). A Manual of Civil Engineering (2nd ed.). London: Griffin Bohn & Company. p. 3.
^ Cite error: The named reference Punmia_etal was invoked but never defined (see the help page).

[1] James, Robert C.; James, Glenn (1992). Mathematics Dictionary. New York: Chapman & Hall. p. 453. ISBN 9780412990410.

[USNBS1960-2] "6 Tables of Interrelation of Units of Measurement". Units of Weight and Measure (United States Customary and Metric): Definitions and Tables of Equivalents (PDF). U.S. Department of Commerce, National Bureau of Standards. 1960. pp. 8–9. (PDF)

[3] Smeaton, John (1837). Reports of the Late John Smeaton, F.R.S. (2nd ed.). London: M Taylor. p. 308. Since the foregoing Report [on the best route for the Forth and Clyde Canal] ... was delivered ... , Mr Smeaton has discovered that, notwithstanding the care and pains he took to be correct, he has committed an error, in supposing the Scotch chain, with which the measures of the length of the tract of land were taken, to consist of seventy feet each, whereas, in reality, it consists of seventy-four

[4] William John Macquorn Rankine (1863). A Manual of Civil Engineering (2nd ed.). London: Griffin Bohn & Company. p. 3.

[Punmia_etal-5] Cite error: The named reference Punmia_etal was invoked but never defined (see the help page).

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