US Survey Acres to Square Miles (ac (US) to mi²)
1 US survey acre equals 0.00156250625 square miles (rounded).
How to convert US survey acres to square miles
To convert US survey acres to square miles, multiply the number of US survey acres by 0.00156250625. The factor is rounded to 10 significant digits. To go the other way, multiply square miles by 639.99744 (rounded).
square miles = US survey acres × 0.00156250625
Example: 10 US survey acres = 0.0156250625 square miles.
About these units
US Survey Acre (ac (US))
43,560 square US survey feet (about 4,046.873 m²), slightly larger than the international acre. Used in US land records until 2022.
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.
1 US survey acre = 4,046.87261 square meters (approximately).
Sources: Wikipedia: Acre; NIST SP 811 Appendix B.8 (conversion factors)
Square Mile (mi²)
640 acres or about 2.59 km². Used for the area of cities, states and countries in the US and UK.
A thousand Roman paces, mille passus, became the mile, and under Elizabeth I Parliament fixed the statute mile at eight furlongs, or 5,280 feet, in place of the older Roman-based value. The square mile inherits that length. Its most famous use came in the United States: the Land Ordinance of 1785 started the Public Land Survey System so that western land could be surveyed and sold to pay war debts, beginning with the Seven Ranges in eastern Ohio.
In that system a section is roughly one square mile, or 640 acres, and a township is 36 sections in a square six miles on a side. One square mile is nearly 2.59 million square meters. Chicago's Midway International Airport, at about 650 acres, covers roughly 1.02 square miles. Beware the phrase mile square: a region 20 miles square has 400 square miles, but so does a rectangle 10 by 40 miles. The US survey version of the mile was retired from 1 January 2023, but the international square mile remains the unit for cities, states and countries in the US and UK.
1 square mile = 2,589,988.11 square meters (approximately).
Sources: Wikipedia: Square mile; Wikipedia: Public Land Survey System; Wikipedia: Mile
Related conversions
- Square miles to US survey acres (reverse)
- US survey acres to square meters
- US survey acres to square kilometers
- US survey acres to hectares
- US survey acres to square inches
- US survey acres to square feet
- US survey acres to square yards
- US survey acres to acres
- Square meters to square miles
- Square kilometers to square miles
- Hectares to square miles
- Square inches to square miles
- Square feet to square miles
- Square yards to square miles
- Acres to square miles
- Square centimeters to square miles
- Square millimeters to square miles
- Tsubo to square miles
- Pyeong to square miles
- Rai (Thai) to square miles
See all area units.