The hectare (/ˈhɛktɛər/ or /ˈhɛktɑr/; 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. An acre is about 0.4047 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.