A unit of land area, = 100 ares = 10,000 square meters, approximately 2.471054 acres. Symbol, ha.
The are, hectare and their symbols were adopted by the CIPM in 1879.¹ In 1978 the CIPM decided it would be better to express all areas in square meters, and, while the are and hectare could continue to be used for the time being, they should not be introduced where not presently used. In the United States, however, the hectare is still legally considered a unit within SI.
Proc.-Verb. Com. Int. Poids et Mesures, 1879.
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Last revised: 7 February 2006.