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.

Hectare conversion table