A chain is an old unit of length used mainly by surveyors for measuring building blocks, roads, and railways.
A chain is equivalent to 66 feetwarning.png"feet" is not declared as a valid unit of measurement for this property., one tenth of a furlong, or one eightieth of a mile. It is also very close to 20 metres.
A chain is subdivided into 100 links, each nearly eight inches long.
The chain was used for land measures. One square chain (e.g. one chain long by one chain wide) is one tenth of an acre. Many older building blocks were one quarter of an acre, measured as one chain wide by two-and-a-half chains long.
It was also used for railway surveying, with distances being measured in miles and chains, or miles, chains, and links, and curves measured in chains.
Many road and railway easements were designed as multiples of one chain wide.
One chain is the length of a cricket pitch.
Surveyors carried an actual chain composed of 100 links, and this is the source of the name of the measures.