Fermanagh Gold Introduction
 
UNITS OF MEASUREMENT

Thanks to Phil for sending a definitive guide to measurements used in various land documents.

Acre
The (English) acre is a unit of area equal to 43,560 square feet, or 10 square chains, or 160 square poles. It derives from a plowing area that is 4 poles wide and a furlong (40 poles) long. A square mile is 640 acres. The Scottish acre is 1.27 English acres. The Irish acre is 1.6 English acres.

Chain
Unit of length usually understood to be Gunter's chain, but possibly variant by locale. The name comes from the heavy metal chain of 100 links that was used by surveyors to measure property bounds.

Colpa
Old Irish measure of land equal to that which can support a horse or cow for a year. Approximately an Irish acre of good land.

Furlong
Unit of length equal to 40 poles (220 yards). Its name derives from "furrow long", the length of a furrow. See Gunter's chain.

Gunter's Chain
Unit of length equal to 66 feet, or 4 poles. This unit was apparently defined as one tenth of a furlong, a common unit of length in the old days. The mile was redefined from the old Roman value of 5000 feet to 5280 feet in order to be an even multiple of furlongs. A mile is 80
chains.

Link
Unit of length equal to 1/100 chain (7.92 inches).

Perch 
See pole

Pole
Unit of length and area. Also known as a perch or rod. As a unit of length, equal to 16.5 feet. A mile is 320 poles. As a unit of area, equal to a square with sides one pole long. An acre is 160 square poles. It was common to see an area referred to as "87 acres, 112 poles", meaning 87 and 112/160 acres.

Rod
See pole

Rood
Unit of area usually equal to 1/4 acre