US Survey Acres to Square Kilometers (ac (US) to km²)

1 US survey acre equals 0.00404687261 square kilometers (rounded).

1 US survey acre = 0.00404687261 square kilometers

How to convert US survey acres to square kilometers

To convert US survey acres to square kilometers, multiply the number of US survey acres by 0.00404687261. The factor is rounded to 10 significant digits. To go the other way, multiply square kilometers by 247.104393 (rounded).

square kilometers = US survey acres × 0.00404687261

Example: 10 US survey acres = 0.0404687261 square kilometers.

About these units

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.

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 Kilometer (km²)

Metric (SI)Current unit

One million square meters (100 hectares). Used for the area of cities, countries and lakes.

Metric land measure took a surprisingly long time to settle on the kilometer. The meter was defined in 1799, yet people initially preferred the myriameter, 10,000 meters, and the French phrase myriamètres par heure was still in print in 1802. The Netherlands adopted the kilometer in 1817 under the name mijl. Once the kilometer was established, the square kilometer followed naturally as the unit for areas too large to count comfortably in hectares or square meters.

One square kilometer is 1,000,000 square meters, or 100 hectares, about 0.3861 square miles or 247.1 acres. A useful picture comes from history: many medieval European cities were enclosed by walls around roughly a square kilometer, with Delft at about 0.9 km² and Lucca at about 1.09 km². A standard 18-hole golf course of 6,000 meters needs about 0.8 km². The symbol km² means the square of a kilometer, not a thousand square meters. The planned Square Kilometre Array radio telescope takes its name from the collecting area it aims for.

1 square kilometer = 1,000,000 square meters (exactly).

Sources: Wikipedia: Square kilometre; Wikipedia: Kilometres per hour

Related conversions

See all area units.