1 ha = 10 4 m 2 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 km 2. 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.