Information about Perch (unit)

The rod is a unit of length, equal to 5.5 yards, 11 cubits, 5.0292 metres, 16.5 feet, or ¹⁄₃₂₀ of a statute mile. A rod is the same length as a perch^[1] and a pole. The lengths of the perch (one rod) and chain (four rods) were standardized in 1607 by Edmund Gunter.

The length is equal to the standardized length of the ox goad used by medieval English ploughmen; fields were measured in acres which were one chain (four rods) by one furlong (in the United Kingdom, ten chains).

Because the furlong was "one plough's furrow long" and a furrow was the length a plough team was to be driven without resting, the length of the furlong and the acre vary regionally, nominally due to differing soil types. In England the acre was 4,840 square yards, but in Scotland it was 6,150 square yards and in Ireland 7,840 square yards. In all three countries, fields were divided in acres and thus the furlong became a measure commonly used in horse racing, archery, and civic planning.



Bars of metal one rod (16.5 feet) long were used as standards of length in surveying land in the past. One example of a surveyor's rod is a one piece metal bar encased in a cylindrical canvas tube (to keep the sun from heating it and making it increase in length) with a piece of the semiprecious gemstone jasper at each end of the rod (to prevent wear of the metal bar).

The rod is still in use as a unit of measure in certain specialised fields. In recreational canoeing, maps measure portages (overland paths where canoes must be carried) in rods. This is thought to persist due to the rod approximating the length of a typical canoe. In the United Kingdom, the sizes of allotment gardens continue to be measured in rods. In Vermont, the default width of state and town highways and trails is three rods. (VSA Title 17 §702)

The rod was still in use as a common unit of measurement in the mid-1800s, when Henry David Thoreau used it frequently when describing distances in his work Walden.

Notes

See also

• furlong
• perch (volume) for a related unit of volume with the same name.

Popular culture and trivia

• In the episode of The Simpsons entitled ‘A Star Is Burns’, Grampa Simpson uttered: “My car gets forty rods to the hogshead, and that's the way I likes it!” That translates into 504 U.S. gallons per mile, or about 1.2 litres per metre! In units more normal for this purpose, it is 0.00198 miles per US gallon (or about 10.48 feet per gallon) or 118,500 L/100 km.
• Passenger automobiles, especially those marketed globally, commonly measure about one rod in length. Within the industry, "five meter car" is a term used for a car whose overall length approaches but does not exceed 5 meters, or almost exactly 1 rod. In particular, the term signifies a car designed with export in mind. 5 meters is the standard vehicle length limit for efficient packing inside the cargo ships that transport cars.
• Similarly, the minimum standard height clearance for a road bridge is around 1 rod (in the UK it's 16' 3"); any less, and it must be marked as a "low bridge" with warning signs.