Chain (unit of length)

Definitions and variants

There are multiple historical definitions of a chain, ranging from about 50 feet up to 100 feet. The best known form, the surveyor's or Gunter's chain, is 66 feet long (20.1168 metres) and is divided into 100 links; each link is 0.66 feet (7.92 inches). Another common standard, the engineer's chain, measures 100 feet and was used where decimal-friendly lengths were preferred. These variants are described under different names in old surveying manuals and legal texts (for example, see historical standards and survey practice).

Measurements and conversions

• 1 Gunter's chain = 66 feet = 22 yards = 20.1168 m (conversion)
• 1 chain = 100 links (each link = 7.92 in ≈ 0.201168 m)
• 1 chain = 4 rods (a rod = 16.5 feet)
• 10 square chains = 1 acre (a rectangle 1 chain by 10 chains = 43,560 ft²)
• 10 chains = 1 furlong; 80 chains = 1 mile

History and development

The standardized Gunter's chain was introduced in the early 17th century by Edmund Gunter to simplify land measurement and computation. By fixing a chain at 66 feet and dividing it into 100 links, surveyors could easily compute areas and lengths in acres and furlongs using simple arithmetic. Chains and linked measuring tools remained widespread in the United Kingdom, North America, Australia and elsewhere until the 20th century, when electronic instruments and metrication gradually displaced them. Historical maps and many legal property descriptions still refer to chains, links and rods (legal context).

Uses and legacy

Although modern surveying relies on total stations, GPS and metric units, the chain has left a lasting imprint. Property deeds, older land surveys, boundaries and some road measurements preserve chain-based distances. Understanding the chain is therefore important for interpreting historical documents, reconciling old surveys with modern plans, and for specialized surveying tasks. For practical examples and archival guidance see general references on land measurement and surveying practice (conversion notes, survey history).