Acres to Square Miles
Type a value in either box to convert between acres and square miles. The factor is 0.0015625.
| Acres | Square Miles |
|---|---|
| 1 ac | 0.001563 mi² |
| 2 ac | 0.003125 mi² |
| 3 ac | 0.004688 mi² |
| 5 ac | 0.007812 mi² |
| 10 ac | 0.015625 mi² |
| 25 ac | 0.039062 mi² |
| 50 ac | 0.078125 mi² |
| 100 ac | 0.15625 mi² |
How to use
- Enter a value in the Acres field.
- The Square Miles figure appears immediately — no button to press.
- Typing in the Square Miles field converts back to Acres the same way.
- Use the reference table for the values that come up most often.
Acres to Square Miles formula
To convert acres to square miles, multiply by 0.0015625.
mi² = ac × 0.0015625
Put another way, one acre is exactly 1/640 of a square mile.
Why this factor: the acre and the square mile are both defined against the square meter, so dividing one definition by the other gives 0.0015625 directly. Both definitions are set out in full below.
To go the other way, divide by 0.0015625 — or use the Square Miles to Acres converter, which is the same calculation reversed.
Worked example
Take 250 ac and multiply by the factor 0.0015625: the result is 0.390625 mi².
250 ac × 0.0015625 = 0.390625 mi²
The converter above does this for any value you type, in either direction.
What is an acre?
An acre is the customary land area unit of the US and UK, historically a day's ploughing for one team of oxen.
Definition: One chain by one furlong — 43,560 square feet — which is exactly 4,046.8564224 square meters.
Where it is used: US and UK property and farmland, development parcels, and land sales.
Worth knowing: 640 acres make one square mile, the basis of the US Public Land Survey grid.
What is a square mile?
A square mile is the area of a one-mile square, used for large land areas in the US and UK.
Definition: Exactly 2,589,988.110336 square meters, and exactly 640 acres.
Where it is used: County, state and metropolitan areas, and population density in the US.
Acres vs Square Miles
The acre and the square mile belong to the same family of units, so converting between them is usually a matter of shifting a decimal point or applying a small whole-number factor.
Frequently asked questions
How many square miles are in an acre?
One acre equals 0.0015625 square miles.
What is the formula to convert acres to square miles?
Multiply the number of acres by 0.0015625. To reverse it, divide by 0.0015625 instead.
How do I convert square miles back to acres?
Divide by 0.0015625, which is the same as multiplying by 640.
How many square miles are in 10 acres?
10 ac works out to 0.015625 mi².
Is there anything to watch out for with acres?
640 acres make one square mile, the basis of the US Public Land Survey grid.
How is the acre defined?
One chain by one furlong — 43,560 square feet — which is exactly 4,046.8564224 square meters.