Conversion from 25 Hectares to Decares

Information about the Hectare (ha)

The hectare is a unit of area equal to 10,000 square metres, written ha. It is a square one hundred metres on a side. It is not strictly an SI unit, but the International Bureau of Weights and Measures accepts it for use with the SI in the one field where it is indispensable: the measurement of land.

It descends from the are, a unit of one hundred square metres introduced in revolutionary France in 1795. The are proved too small for fields and the square kilometre too large, so the hundredfold multiple settled into the gap and outlived its parent entirely. Today almost nobody writes ares, while hectares appear on title deeds, farm subsidies and environmental reports across most of the world.

Agriculture is built on it. Crop yields are quoted in tonnes per hectare, and the figures carry a great deal of information in very little space: wheat in north-western Europe runs to about eight tonnes per hectare, against a world average nearer three. Wine appellations cap production in hectolitres per hectare, and European farm support has been paid per hectare rather than per tonne since the 1990s, which changed what farmers grew as much as any agronomic advance.

Environmental accounting uses the same unit. Deforestation, wetland loss, protected area and reforestation targets are all reported in hectares, because the quantity is large enough to describe a forest and small enough to describe a field. Urban planning uses it inverted, as dwellings per hectare, which is the standard way of comparing the density of one development with another.

For a sense of scale, an association football pitch of the usual size covers about 0.7 hectares, so a hectare is roughly a pitch and a half. A hectare of productive farmland feeds a handful of people on a mixed diet, and a hectare of dense city holds several hundred residents. Traditional Japanese and Korean land measures happen to land close by: one chō and one jeongbo are both about 0.99 hectares.

The imperial competitor is the acre, and the two do not convert cleanly: one hectare is 2.471 acres, and one acre is 0.4047 hectares. Where both systems are in use, as in Ireland, parts of Canada and much of South Asia, land is often quoted in both, and the conversion factor is one of the few worth committing to memory.

One hectare equals 10,000 square metres, about 2.471 acres, 0.01 square kilometres, or about 107,639 square feet.

Information about the Decare (daa)

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.