US Survey Acre (ac (US))

US land surveyHistorical unit (no longer in standard use)

43,560 square US survey feet (about 4,046.873 m²), slightly larger than the international acre. Used in US land records until 2022.

1 US survey acre = 4,046.87261 square meters (approximately).

About the US survey acre

Two acres existed side by side in the United States for decades, separated by a tiny difference in the definition of the foot. Both contain 43,560 square feet, but the international acre uses the foot fixed in 1959 from a yard of exactly 0.9144 meter, giving 4,046.8564224 square meters. The survey acre keeps the older relation set by the 1893 Mendenhall Order, in which one meter is exactly 39.37 inches, giving about 4,046.873 square meters.

The gap is only about 0.016 square meter, roughly 160 square centimeters, but across a large state it adds up to real discrepancies, which is why surveyors held on to the old figure for land records. In October 2019 the National Geodetic Survey and NIST announced that the temporary continued use of the survey foot, mile and acre would end at the close of 2022, and the international units are meant to replace them. The acre itself began as the land a farmer with oxen could plough in a day, and its name comes from an Old Norse word for cultivated land.

Sources: Wikipedia: Acre; NIST SP 811 Appendix B.8 (conversion factors)

US Survey Acre conversion chart

1 US survey acre expressed in every other area unit:

More US land survey units

• section (area)
• township (area)
• US survey foot (length)
• US survey mile (length)

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