Chain
Length · Also called: Gunter’s chain, link
That is
20.12 m
1 chain (Gunter’s chain)
The other way round: 1 km is 49.7097 chains.
- Period: 1620 to today as an archaic unit
- Region: the UK and the Empire
- Goods: land survey, railways
Values
| Value | That is | Period | Used for |
|---|---|---|---|
| Gunter’s chain | 20.12 m | 1620 to today as an archaic unit | land survey, railways · the UK and the Empire |
| link | 20.12 cm | 1620 onwards | the UK and the Empire |
What the unit was used for
The chain is engineered, not inherited: Edmund Gunter, an English clergyman and mathematician, designed it in 1620 as a physical chain of 100 links of 7.92 inches joined by rings.
Its length reconciles two incompatible habits, because surveyors wanted to calculate in decimals while the law recognised rods, furlongs and acres.
A chain is four rods, so ten square chains make exactly one acre, ten chains a furlong and eighty chains a mile, while the hundred links keep the arithmetic decimal.
Chain and link became statutory measures across Britain and the Empire, and the chain is why a cricket pitch is 22 yards and why British railway mileposts still read in miles and chains.
In the system
1 chain = 100 links = 4 rods = 22 yards; 10 chains = 1 furlong; 80 chains = 1 mile