| Hectares (ha) | Square centimeters (cm²) |
|---|---|
| 1 Hectare | 100000000 cm² |
| 2 Hectares | 200000000 cm² |
| 3 Hectares | 300000000 cm² |
| 4 Hectares | 400000000 cm² |
| 5 Hectares | 500000000 cm² |
| 10 Hectares | 1000000000 cm² |
| 20 Hectares | 2000000000 cm² |
| 25 Hectares | 2500000000 cm² |
| 50 Hectares | 5000000000 cm² |
| 100 Hectares | 10000000000 cm² |
| Reference | Hectares (ha) | Square centimeters (cm²) |
|---|---|---|
| A sheet of A4 paper | 0.000006237 ha | 623.7 cm² |
| A tennis court | 0.02608 ha | 2608000 cm² |
| A football pitch | 0.714 ha | 71400000 cm² |
| One hectare | 1 ha | 100000000 cm² |
| Central Park, New York | 341 ha | 3.41 × 1010 cm² |
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.
The square centimetre is a unit of area equal to one ten-thousandth of a square metre, written cm². It is the area of a square one centimetre on a side, and it contains one hundred square millimetres. It is the working unit for anything the size of a hand or smaller: wounds, printed circuits, laboratory cultures, sensor chips and postage stamps.
The arithmetic catches people out. Because area scales with the square of length, one hundred square centimetres make a square decimetre and ten thousand make a square metre, not one hundred. A square ten centimetres on a side is 100 cm², and doubling its side to twenty centimetres gives 400 cm², not 200. Nearly every mistake made with this unit comes from applying the linear factor instead of the squared one.
Medicine measures skin in it. Wounds, ulcers, burns and skin lesions are recorded in square centimetres so that healing can be tracked as a shrinking number over weeks, and dermatological treatments are dosed by the area treated. A typical adult palm covers roughly 100 square centimetres, which is why the palm is used as a rough field estimate of burn extent.
Laboratories rely on it for cell culture. Flasks are named by their growth surface, so a T25 offers 25 square centimetres and a T75 offers 75, and cell densities are counted per square centimetre. Photovoltaic research reports efficiency on cells of exactly one square centimetre, precisely so that results from different laboratories describe the same thing.
Engineering uses it for pressure in some traditions. The kilogram-force per square centimetre, close to one atmosphere, is still printed on tyre gauges, pressure vessels and hydraulic equipment in Japan, Korea and parts of eastern Europe, and it survives because the number it produces is conveniently near the values people already knew. Printed circuit boards are quoted and priced by the square centimetre for the same practical reason.
Against the imperial system it faces the square inch, which is 6.4516 square centimetres exactly. That factor comes straight from the inch being defined as exactly 2.54 centimetres, so unlike most imperial conversions this one is not an approximation, merely an awkward number.
One square centimetre equals 100 square millimetres, 0.0001 square metres, or about 0.155 square inches.