Rod (unit)

rod
rod
Unit system	imperial/US units
Unit of	length
Conversions
1 rod in ...	... is equal to ...
Imperial/US units	16+1⁄2 ft
metric (SI) units	5.0292 m

The rod, perch, or pole (sometimes also lug) is a surveyor's tool^[1] and unit of length of various historical definitions. In British imperial and US customary units it is defined as 16+1⁄2 feet, equal to exactly 1⁄320 of a mile, or 5+1⁄2 yards (a quarter of a surveyor's chain), and is exactly 5.0292 meters. The rod is useful as a unit of length because integer multiples of it can form one acre of square measure (area). The 'perfect acre'^[2] is a rectangular area of 43,560 square feet, bounded by sides 660 feet (a furlong) long and 66 feet (a chain) wide (220 yards by 22 yards) or, equivalently, 40 rods by 4 rods. An acre is therefore 160 square rods or 10 square chains.

The name perch derives from the Ancient Roman unit, the pertica. The measure also has a relationship with the military pike of about the same size. Both measures^[1] date from the sixteenth century,^[3] when the pike was still utilized in national armies. The tool has been supplanted, first by steel tapes and later by electronic tools such as surveyor lasers and optical target devices for surveying lands. In dialectal English the term lug has also been used, although the Oxford English Dictionary states that this unit, while usually of 16+1⁄2 feet, may also be of 15, 18, 20, or 21 feet.^[4]^[5]^[6]

In the United States until 1 January 2023, the rod was often defined as 16.5 US survey feet, or approximately 5.029 210 058 m.^[7]

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^ "lug, n.1". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
^ "U.S. Survey Foot: Revised Unit Conversion Factors". National Institute of Standards and Technology. 23 September 2019. Retrieved 3 January 2023.

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[OED-lug-6] "lug, n.1". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)

[7] "U.S. Survey Foot: Revised Unit Conversion Factors". National Institute of Standards and Technology. 23 September 2019. Retrieved 3 January 2023.

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