| Reference | Chains (ch) | Yards (yd) |
|---|---|---|
| A sheet of A4 paper (long side) | 0.0147638 ch | 0.324803 yd |
| Average adult human height | 0.0845065 ch | 1.85914 yd |
| A football pitch (length) | 5.21952 ch | 114.829 yd |
| A marathon | 2097.5 ch | 46145 yd |
| Height of Mount Everest | 439.881 ch | 9677.38 yd |
The chain is a unit of length equal to 66 feet, 22 yards, or exactly 20.1168 metres. It occupies an unusual position in the imperial system as the unit that connected everyday measurement to land surveying.
It is named after a physical object. Edmund Gunter, an English mathematician, introduced a surveying chain of 100 iron links in 1620. The design solved a real problem: land area was recorded in acres, a unit inherited from medieval agriculture, while distances were measured in feet and yards. Gunter chose a length that reconciled the two systems. Ten square chains make exactly one acre, and 80 chains make one mile, so a surveyor could measure in chains and compute both area in acres and distance in miles without awkward conversion factors.
The chain shaped the landscape of several countries. The United States Public Land Survey System, which divided much of the American west into townships and sections from 1785, was laid out in chains. A section is one square mile, or 80 chains on a side, and the resulting grid remains visible in road patterns and field boundaries across the Midwest. Similar surveys in Canada, Australia and New Zealand used the same unit, and older property deeds in those countries still cite chain measurements.
Cricket preserves it in sporting form. The pitch measures 22 yards between the wickets, which is exactly one chain, a length fixed long before the game's laws were formally written.
British railways continue to use the chain for locating features along a line. Positions are recorded as a mileage and a chain figure, so 12 miles 40 chains identifies a point precisely. The convention survives in signalling diagrams and engineering records despite general metrication.
The chain subdivides into 100 links of 7.92 inches each, giving surveyors a decimal subdivision within an otherwise non-decimal system.
One chain equals 22 yards, 66 feet, or 20.1168 metres.
The yard is a unit of length equal to exactly 0.9144 metres, or three feet. The symbol is yd. It is the base unit of the imperial and United States customary length systems, with the foot and inch defined as fractions of it.
That relationship is the reverse of what most people assume. Since 1959 the yard has been defined against the metre, and the foot and inch follow from it, so every imperial length unit is ultimately derived from an SI definition. The International Yard and Pound Agreement fixed the value at 0.9144 metres exactly, reconciling small differences between the American and British yards that had persisted for decades.
The origin of the name is uncertain. Old English gierd meant a rod or measuring stick. The frequently repeated story that Henry I defined the yard as the distance from his nose to his outstretched thumb is not supported by contemporary evidence, though it has proved durable. A physical standard yard bar was maintained in London from 1760, and its destruction in the 1834 Palace of Westminster fire forced a lengthy reconstruction from surviving copies.
Sport keeps the unit prominent. An American football field is 100 yards between goal lines, and the game's vocabulary is built around yardage. Golf course distances are marked in yards in Britain and the United States. Cricket sets the distance between wickets at 22 yards, a figure inherited from the surveyor's chain.
Fabric and carpet are sold by the yard in the United States, and textile widths are quoted in inches alongside. Landscaping materials such as topsoil and gravel are sold by the cubic yard, which is 27 cubic feet or about 0.7646 cubic metres.
Its cube runs the construction trade in North America. Concrete is ordered, delivered and billed by the cubic yard, about 0.765 cubic metres, and a standard mixer truck carries eight or nine of them; excavation, gravel, topsoil and demolition waste are all quoted the same way. Golf keeps the linear unit just as firmly, with every hole on every scorecard measured in yards and every club sold on the distance it carries, so a player who reads a shot as a hundred and fifty yards is using a measurement the rest of the game's arithmetic depends on. Between them the two uses make the yard unlikely to disappear.
One yard equals 3 feet, 36 inches, or 0.9144 metres exactly. It is a little shorter than a metre, by about 8.4 centimetres.