British land was traditionally measured by how much ground a team of eight oxen could plough in a day. That is an acre, and it is why an acre is a long thin shape of one furlong by one chain rather than a square. The oxen did not get a tea break.
Acre (ac)
Historically the amount of land a team of eight oxen could plough in one day. Approx. 4,840 square yards. Still used in the UK for land measurement.
4,046.86 square metres
Carucate
The Danelaw equivalent of the hide, defined as the land a plough team of eight oxen could work through a full year.
Approx. 120 acres = 485,623 square metres
Erw (Welsh Acre)
The Welsh acre, set out in the tenth-century Laws of Hywel Dda and defined by the reach of a ploughman’s goad rather than by a day’s work.
Approx. 4,320 square yards = 3,612 square metres
Hectare (ha)
Ten thousand square metres, being a square of one hundred metres on each side, and the metric standard for agricultural land.
10,000 square metres = 2.4711 acres
Hide
A variable medieval land unit of approximately 120 acres, notionally sufficient to support a single peasant household.
Approx. 120 acres = 485,623 square metres
Irish Acre
Seven thousand eight hundred and forty square yards, being the acre as reckoned on the Irish perch of seven yards.
7,840 square yards = 6,555 square metres = 1.62 English acres
Oxgang / Bovate
The share of land attributed to a single ox within an eight-beast plough team, being one eighth of a carucate.
Approx. 15 acres = 60,703 square metres
Perch (Channel Islands)
A fortieth of a vergée, and the working subdivision of Channel Islands land measurement.
Jersey: approx. 44.7 m². Guernsey: approx. 39.4 m²
Rood
One-quarter of an acre, traditionally used for measuring small land plots and gardens.
1,011.71 square metres
Square Mile (mi²)
The largest customary imperial area unit, containing exactly 640 acres.
640 acres = 2.59 square kilometres
Square Perch
The square of a perch of 16½ feet, being 30¼ square yards. Forty square perches make one rood.
30¼ square yards = 25.29 square metres
Sulung
The Kentish unit of land assessment, reckoned at roughly two hides, and divided into four yokes.
Approx. 240 acres = 97 hectares
Vergée
The traditional land measure of Jersey and Guernsey, descended from Norman French practice and still in current use.
Jersey: approx. 0.44 acres = 1,786 m². Guernsey: approx. 0.39 acres = 1,576 m²