| Decares (daa) | Deciares (da) |
|---|---|
| 1 Decare | 100 da |
| 2 Decares | 200 da |
| 3 Decares | 300 da |
| 4 Decares | 400 da |
| 5 Decares | 500 da |
| 10 Decares | 1000 da |
| 20 Decares | 2000 da |
| 25 Decares | 2500 da |
| 50 Decares | 5000 da |
| 100 Decares | 10000 da |
| Reference | Decares (daa) | Deciares (da) |
|---|---|---|
| A sheet of A4 paper | 0.00006237 daa | 0.006237 da |
| A tennis court | 0.2608 daa | 26.08 da |
| A football pitch | 7.14 daa | 714 da |
| One hectare | 10 daa | 1000 da |
| Central Park, New York | 3410 daa | 341000 da |
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 deciare is a unit of area equal to one tenth of an are, or ten square metres. Its symbol is da. It completes the decimal ladder that the French metric law of 1795 built around the are, alongside the centiare below it and the hectare above, but unlike either of those it never found a job and is today the least used member of the family.
Ten square metres is an easily pictured quantity. It is a small bathroom, a single bedroom in a modest flat, or four fifths of a car parking space. It is the floor of a garden shed, the area a market trader is allotted at a fair, or the footprint of a large dining table with chairs pushed back. Nothing about the size is obscure; only the name is.
The reason it failed is structural. Land registration adopted a three-column system running hectare, are and centiare, each step a factor of one hundred, which mirrors how areas actually behave: squaring a tenfold change in length produces a hundredfold change in area. A tenth of an are sits between two columns and belongs to neither, so no register ever needed a place for it.
Its symbol makes matters worse. In the International System, da is the prefix symbol for deca, so a reader meeting da in a technical document is far more likely to take it as the start of a compound like dam or daN than as a unit in its own right. The decare, ten times larger, is written daa, which does nothing to help.
Where the quantity does need naming, ordinary metric notation handles it without effort. Ten square metres is written 10 m², which is shorter than one deciare, needs no explanation, and sorts correctly beside every other figure on a plan or in a contract.
The unit therefore survives almost entirely in conversion tables and in teaching material that runs through the complete prefix ladder. Encountering it in a real document usually means the document is old, translated from an older source, or reproducing a table rather than making a measurement, and converting it to square metres at once is the safe response.
One deciare equals 10 square metres, 0.1 ares, 0.001 hectares, or about 107.6 square feet.