Convert Square Miles to Acres
Square miles to acres is the conversion you need whenever land is measured in square miles but you want it in the acre figures used for farms and lots. One square mile is exactly 640 acres, so the number gets much larger when you switch from square miles to acres.
Square miles to Acres conversion table
| Square miles (mi²) | Acres (ac) |
|---|---|
| 1 | 640 |
| 2 | 1,280 |
| 3 | 1,920 |
| 5 | 3,200 |
| 10 | 6,400 |
| 20 | 12,800 |
| 50 | 32,000 |
| 100 | 64,000 |
| 500 | 320,000 |
| 1,000 | 640,000 |
The formula
To convert square miles to acres, multiply the number of square miles by 640:
acres = square miles × 640
A worked example
Say you have 5 square miles of land and want it in acres:
5 × 640 = 3,200 acres
So 5 square miles works out to 3,200 acres.
Why the number is exact
A square mile is defined as exactly 640 acres — this is baked into the US Public Land Survey System, where one square mile is a "section" of 640 acres. Because it's a defined relationship rather than a measured one, multiplying square miles by 640 always gives an exact result.
When you'll use it
Reading rural and agricultural land figures where acres are the standard, working with US survey descriptions that use sections, and comparing large tracts of land between square-mile and acre measurements.
Frequently asked questions
How many acres are in a square mile?
Exactly 640 acres. It's an exact whole number, and in the US Public Land Survey System a square mile is called a 'section,' which is defined as exactly 640 acres.
Is the square miles to acres conversion exact?
Yes. A square mile equals exactly 640 acres by definition, so there's no rounding — multiply the square miles by 640 and you get an exact answer.
What is a 'section' of land?
A section is the survey term for one square mile of land in the US Public Land Survey System, and it equals exactly 640 acres. It's the reason square miles and acres line up so cleanly.