<Tr> <Th> Symbol </Th> <Td> ha </Td> </Tr> <Tr> <Th> In SI base units: </Th> <Td> 1 ha = 10 m </Td> </Tr> <P> The hectare (/ ˈhɛktɛər, - tɑːr /; SI symbol: ha) is an SI accepted metric system unit of area equal to 100 ares (10,000 m) or 1 square hectometre (hm) 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 . </P> <P> 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 ​ ⁄ km . 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". </P>

100 acres is equal to how many hectares