Editing Rod (unit) (section)

{{short description|Unit of length}}
{{distinguish|text = a [[Pole (surveying)|surveyor's pole]], upon which a survey instrument is mounted; a [[ranging rod]] used for sighting; or, a [[level staff]], which may also be called a leveling rod}}
{{Use dmy dates|date=January 2023}}
{{Use American English|date=March 2021}}

{{Infobox unit
| name     = rod
| standard = [[imperial units|imperial]]/[[US customary units|US]]&nbsp;units
| quantity = [[length]]
| units1   = Imperial/US&nbsp;units
| inunits1 = {{frac|16|1|2}}&nbsp;[[Foot (unit)|ft]]
| units2   = [[metric system|metric]] ([[SI]]) units
| inunits2 = 5.0292 m
}}

The '''rod''', '''perch''', or '''pole''' (sometimes also '''lug''') is a [[surveying|surveyor's]] tool<ref name="Connections"/> and [[unit of length]] of various historical definitions. In [[Imperial units|British imperial]] and [[United States customary units|US customary units]], it is defined as {{frac|16|1|2}} [[Foot (unit)|feet]], equal to exactly {{frac|1|320}} of a [[mile]], or {{frac|5|1|2}} [[yard]]s (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'<ref name="Connections0"/> is a rectangular area of 43,560 square feet, bounded by sides 660 feet (a [[furlong]]) long and 66 feet (a [[Chain (unit)|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 units of measurement|Ancient Roman unit]], the ''[[pertica (unit)|pertica]]''.
The measure also has a relationship with the military [[pike (weapon)|pike]] of about the same size. Both measures<ref name="Connections"/> date from the sixteenth century,<ref name="Connections2"/> when the pike was still utilized in national armies. The tool has been supplanted, first by [[Tape measure|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 {{frac|16|1|2}} feet, may also be of 15, 18, 20, or 21 feet.<ref name=bonten/><ref name="dict-lug"/><ref name=OED-lug>{{Cite OED|lug, n.1}}</ref>

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.<ref>{{Cite web| title = U.S. Survey Foot: Revised Unit Conversion Factors | website = National Institute of Standards and Technology| date = 23 September 2019| accessdate = 3 January 2023| url = https://www.nist.gov/pml/us-surveyfoot/revised-unit-conversion-factors}}</ref>