Land Measurement Quick Reference, What's a Rod? What's a Gunter's Chain?

12 inches = 1 foot
144 sq. inches = 1 square foot
3 feet = 1 yard
9 sq. feet = 1 square yard
220 yards = 1 furlong
4840 sq. yards = 1 acre
8 furlongs = 1 mile
640 acres = 1 square mile
5280 feet = 1 mile
1 sq.mile = 1 section
1760 yards = 1 mile
36 sections = 1 Township
1 section = 640 acres
1/2 section = 320 acres
1/4 section = 160 acres
1/2 of 1/4 section = 80 acres
1/4 of 1/4 section = 40 acres
1 side of a section = 1 mile
1 mile = 5,280 feet = 320 rods = 80 chains
1 rod = 16.5 feet
1 chain = 66 feet = 4 rods
43,560 square feet = 1 acre

Encyclopedia Britannica defines a Rod, as an old English measure of distance equal to 16.5 feet (5.029 metres), with variations from 9 to 28 feet (2.743 to 8.534 metres) also being used. It was also called a perch or pole. The word rod derives from Old English rodd and is akin to Old Norse rudda (“club”). Etymologically rod is also akin to the Dutch rood which referred to a land area of 40 square rods, equal to one-quarter acre, or 10,890 square feet (1,012 square metres). It also denoted just one square rod, or 272.25 square feet (25.29 square metres). The rood also was a British linear unit, containing 660 feet (201.2 metres).

Encyclopedia Britannica defines a Surveyor’s chain, also called Gunter’s chain, measuring device and arbitrary measurement unit still widely used for surveying in English-speaking countries. Invented by the English mathematician Edmund Gunter in the early 17th century, Gunter’s chain is exactly 22 yards (about 20 m) long and divided into 100 links. In the device, each link is a solid bar. Measurement of the public land systems of the United States and Canada is based on Gunter’s chain. An area of 10 square chains is equal to one acre.