| Decares (daa) | Square furlongs (sq fur) |
|---|---|
| 1 Decare | 0.0247105381467 sq fur |
| 2 Decares | 0.0494210762934 sq fur |
| 3 Decares | 0.0741316144401 sq fur |
| 4 Decares | 0.0988421525869 sq fur |
| 5 Decares | 0.123552690734 sq fur |
| 10 Decares | 0.247105381467 sq fur |
| 20 Decares | 0.494210762934 sq fur |
| 25 Decares | 0.617763453668 sq fur |
| 50 Decares | 1.23552690734 sq fur |
| 100 Decares | 2.47105381467 sq fur |
| Reference | Decares (daa) | Square furlongs (sq fur) |
|---|---|---|
| A sheet of A4 paper | 0.00006237 daa | 0.0000015412 sq fur |
| A tennis court | 0.2608 daa | 0.00644451 sq fur |
| A football pitch | 7.14 daa | 0.176433 sq fur |
| One hectare | 10 daa | 0.247105 sq fur |
| Central Park, New York | 3410 daa | 84.2629 sq fur |
The decare is a unit of area equal to ten ares, or one thousand square metres. Its symbol is daa. Ten decares make one hectare. Unlike the other members of the are family it is in daily commercial use, though under several different names, because it happened to match land measures that a number of countries were already using when they went metric.
Norway is the clearest case. The Norwegian mål was redefined as exactly one thousand square metres in the metrication of the late nineteenth century, and dekar has been the working unit of Norwegian farming and forestry ever since. Agricultural statistics, subsidy applications and farm sale advertisements are all written in dekar, and a typical Norwegian holding runs to a few hundred of them.
The eastern Mediterranean tells a similar story with different words. The Greek stremma became one thousand square metres on metrication in 1899, the Turkish dönüm was fixed at the same figure, and the metric dunam of Israel, Jordan and Iraq matches both. Bulgaria uses the decare directly, and its farm census is published in it. In each of these places a traditional unit of roughly this size was rounded to the metric value rather than abolished.
The reason it works is that a thousand square metres suits smallholdings. A hectare is a large field, and a hundred square metres is a garden; the decare falls between them, at about the size of an orchard plot, a vineyard parcel or a village building lot. It is also close to a quarter of an acre, which is why it reads naturally to people brought up with either system.
Reporting to international bodies converts it away. European Union agricultural returns, the statistics of the Food and Agriculture Organization and most academic work are all in hectares, so national figures in dekar or stremmata are divided by ten before they travel. This is a frequent source of order-of-magnitude errors in translated agricultural reporting, since a farm of 300 dekar is 30 hectares and not 300.
The symbol daa is awkward but unambiguous, being the deca prefix applied to the are. It should not be confused with da, which is the deciare and one hundred times smaller, nor with the prefix symbol da used before other units.
One decare equals 1000 square metres, 10 ares, 0.1 hectares, or about 0.247 acres.
The square furlong is a unit of area equal to ten acres, or 40,468.6 square metres. Its symbol is sq fur. A furlong is 220 yards, an eighth of a mile, so a square furlong is a hundred square chains and sixty-four of them make a square mile. It is one of the tidiest relationships in the imperial system and one of the least used.
The furlong is older than the acre and gave it its shape. The name means furrow long, and it was the distance an ox team was expected to plough before resting and turning. In the open fields of medieval England a furlong was a block of cultivated strips as well as a length, so the word described a place and a measurement at the same time, and the acre was defined as one furlong by one chain because that was what a day's ploughing produced.
That history explains why the square furlong is arithmetically neat but practically absent. Land was allotted in strips and acres, not in blocks a furlong on a side, so the square form never had a use even when the linear one was in daily service. A surveyor who needed ten acres wrote ten acres, and the square furlong was left as an entry in tables.
The length itself has survived by a peculiar route. Horse racing kept it, and races in Britain, Ireland, the United States, Australia and much of Asia are still described in furlongs: a six-furlong sprint, a mile and a half meaning twelve furlongs. Nothing else in modern life uses the unit, but racing uses it constantly, which keeps the word familiar to people who would struggle to say how long it is.
As an area it is a useful size to picture even so. Ten acres is a small farm, a large public park, about fourteen football pitches, or a city block of generous proportions. New York's Central Park covers roughly eighty-four square furlongs. The unit is large enough that anything measured in it is being described as a place rather than a property.
Converting is cleanest through the acre. Multiply by ten for acres, then by 0.4047 for hectares, or use the direct factor of 4.047 hectares to the square furlong. Going the other way, a hectare is about a quarter of a square furlong, which is close enough for rough comparison of old and new land records.
One square furlong equals 10 acres, 100 square chains, about 40,469 square metres, or about 4.047 hectares.