A chain is a surveyors unit of length that equals 66 feet. There are 80 chains in a mile. An acre is 1 chain by 10 chains. The convenience of the chain for land measure arises from the fact that an acre is one [:UnitsOfMeasure:furlong] (a "furrow long") by one chain, and there are 10 chains in a furlong.

Early surveyors used a Gunter's chain to measure distance. The chain, invented in 1620 by Edmund Gunter, consisted of 100 links, each of which was 0.66 feet long. The chain came to be replaced by a metal tape, but the term "chaining" was still used to refer to the process of measuring distance by use of the tape.

See UnitsOfMeasure.