Difference in Measurement
In the international yard and pound agreement of 1959 the United States and five countries of the Commonwealth of Nations defined the length of the international yard to be exactly 0.9144 metres. Consequently, the international acre is exactly 4,046.8564224 square metres.
The U.S. survey acre is about 4,046.872 609 874 252 square metres; its exact value (4046 13,525,426⁄15,499,969 m2) is based on an inch defined by 1 metre = 39.37 inches exactly, as established by the Mendenhall Order. Surveyors in the United States use both international and survey feet, and consequently, both varieties of acre.
Since the difference between the U.S. survey acre and international acre is only about a quarter of the size of an A4 sheet of paper (0.016 square metres, 160 square centimetres or 24.8 square inches), it is usually not important which one is being discussed. Areas are seldom stated to sufficient accuracy for the different definitions to be detectable.
Read more about this topic: Acre
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