Hectare is a non-SI metric unit of area equal to a square with 100-metre sides (1 hm2), or 10,000 m2, and is primarily used in the measurement of land. It is equivalent to 100 ares or 2.47 acres. The metric system of measurement, the International system of units (SI Units), is widely used for quantitative measurements of matter in science and in most countries. However, different systems of measurement existed before the SI system was introduced. Any units used in other system of measurement (i.e. not included in the SI system of measurement), are non-SI units.