The **hectare** (/ˈhɛktɛər, -tɑːr/; SI symbol: **ha**) is a non-SI metric unit of area equal to a square with 100-metre sides (1 hm^{2}), or 10,000 m^{2}, and is primarily used in the measurement of land. There are 100 hectares in one square kilometre. 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