Decare
| Hectare | |
|---|---|
| Unit system | non-SI metric system |
| Unit of | Area |
| Symbol | ha |
| In SI base units: | 1 ha = 104 m2 |
The hectare (/ˈhɛktɛər/ or /ˈhɛktɑːr/; symbol ha) is an SI accepted metric system unit of area equal to 100 ares (10,000 m2) and primarily used in the measurement of land as a metric replacement for the imperial acre. An acre is about 0.405 hectare and one hectare contains about 2.47 acres.
In 1795, when the metric system was introduced, the "are" was defined as 100 square metres and the hectare ("hecto-" + "are") was thus 100 "ares" or 1⁄100 km2. When the metric system was further rationalised in 1960, resulting in the International System of Units (SI), the are was not included as a recognised unit. The hectare, however, remains as a non-SI unit accepted for use with the SI units, mentioned in Section 4.1 of the SI Brochure as a unit whose use is "expected to continue indefinitely".
The metric system of measurement was first given a legal basis in 1795 by the French Revolutionary government. The law of 18 Germinal, Year III (7 April 1795) defined five units of measure:
Although the law defined the length of the metre, there was no practical way of accurately measuring the metre (and hence the are) until 1799 when the first standard metre was manufactured and adopted.
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