Convert square miles to acres

One square mile equals 640 acres. To convert any number of square miles to acres, multiply by 640.

The converter above works in both directions and updates as you type. Below you will find the formula, a worked example and a reference table of common values.

Area conversions carry a trap that catches people who are perfectly comfortable with length: the factor is squared. There are 3.28 feet in a metre but 10.76 square feet in a square metre, and using the linear factor is the most common error in property arithmetic. Beyond that, land is measured in whatever the local convention prescribes — acres, hectares, and across South Asia bigha, katha and gaj — so the same plot is routinely described in two units that need reconciling.

square miles to acres formula

To go the other way, use square mile = acre ÷ 640.

About these units

A square mile is 640 acres, which is why a US Public Land Survey section — one square mile — divides so neatly into quarter-sections of 160 acres.

An acre is 43,560 square feet, historically about the area one person could plough in a day with a yoke of oxen. It is still standard in US and UK land dealings.

Square Mile is also written square miles, sq mi and mi2. Acre is also written acres.

Sources

1. National Bureau of Standards, "Refinement of Values for the Yard and the Pound", Federal Register, 1 July 1959 — the international yard as exactly 0.9144 m and the avoirdupois pound as exactly 0.45359237 kg.