Acres

For centuries, the agriculture has been a hard work that was part of the life of many people, mainly poor and rural people. They were part of a primary sector dependent economy, that needed the crops to feed the armies, the cities, and the lords and owners of that lands. An small part of the crops were for the workers, that had to feed their families and their animals, many times bartering the goods with anothers.

There was no mechanical technologies neither pesticides that would increase the productivity of a crop, and the struggle against nature was harder that nowadays because of the pests, wild animals, rudimentary medicine, ignorance, wars, epidemics, and rudimentary tools.

A plot of a few acres

It was usual that workers get helped of the power of animals like horses or oxen, what increased the productivity of a normal day.

That would suggest that when they had to divide a plot, they'd bear in mind that factor.

At least since the Romans were in Britain, one of the common measure for lands have been the acre -that had been included in the British Imperial Measure System when defined during the XIX centuary-.

According the encyclopedia britannica, an acre is: unit of land measurement in the British Imperial and United States Customary systems, equal to 43,560 square feet, or 160 square rods. One acre is equivalent to 0.4047 hectares (4,047 square metres). Derived from Middle English aker (from Old English aecer) and akin to Latin ager (“field”), the acre had one origin in the typical area that could be plowed in one day with a yoke of oxen pulling a wooden plow.

We've talk in other posts the problem in antiquity of measure the same distances or areas by different people in different places, and in this case there is another factor, the productivity of the animals which plowed the plots, its slopes, the soil type, if had many stones, if it's wet enough, how many hours a day to work, the number of animals used to work, etc.

Curiously, in old Spanish territories, there was a measure unit with a similar meaning, but with different values, probably because of those factors: the Jovada (o yugada): the land that could plow in a day a "yoke" of oxen or mules, corresponding to almost one hectare (9,973 m²), more that the double.

Example of use of acres in technical documents

As long Great Britain expanded around the world and their peasants and farmers emigrated, the use of acres spread simultaneously to divide the vast new lands.

Other European countries like France or Germany had their acre with different values, but when they adopted the International Measure System, its use disappeared.

Nowadays, the acres are used only in a few countries, and many times for rural and inhabitated places of United States, Canada (in some places of Quebec or Louisiana it's possible to find the old French acre (arpent)), Australia, India, Pakistan, Birmania and the United Kingdom - where is no longer official since 2010, but still used in real estate descriptions -.

 List here some equivalences:

1 international acre	4,046.8564224 m2
1 United States survey acre	4,046.87261 m2
1 acre (oficial)	4,047 m2
1 acre (oficial)	0.4047 hectares
1 acre	aprox. 208.71 feet × 208.71 feet = 43,559.8641 square feet = = aprox. 43,560 square feet
1 acre	4,840 square yards
1 acre	10 square chains
1 acre	160 square rods
1 acre	100,000 links
1 acre	160 perches
1 acre	4 roods
1 acre	furlong 220 yards, chain 22 yards (furlong by a chain)
1 acre	1⁄640 = 0.0015625 square miles
1 square mile	1 acre
1 oxgang the amount of land tillable by one ox in a ploughing season. This could vary from village to village	variable, tipically 15 acres
1 virgate the amount of land tillable by two oxen in a ploughing season	variable, tipically 30 acres
1 carucate the amount of land tillable by a team of eight oxen in a ploughing season. This was equal to 8 oxgangs or 4 virgate.	variable, tipically 120 acres
1 Customary acre similar size to the acre described above, but it was subject to considerable local variation	variable
1 Builder's acre In U.S. construction and real estate development. Used to simplify math and for marketing.	40,000 square feet
1 Scottish acre	variable
1 Irish acre	7,840 square yards
1 Cheshire acre	10,240 square yards
1 Roman acre	1,260 square metres
1 arpent it's a pre-metric French unit based on the Roman actus	Historically, in North America: about 3419 square metres In Louisiana, Mississippi, Alabama, and Florida, the official conversion is 1 arpent = 0.84628-acre (3,424.77365-square-metre) In Arkansas and Missouri, the official conversion is 1 arpent = 0.8507-acre (3,442.66076-square-metre) square metres

References:
- http://global.britannica.com/EBchecked/topic/4100/acre
- http://en.wikipedia.org/wiki/Acre
- http://en.wikipedia.org/wiki/Arpent
- http://en.wikipedia.org/wiki/Oxgang