About the mi² to ac calculation
One square mile is exactly 640 acres, so converting between them is a single multiplication. Enter any value above and the result updates as you type. Used for land and territory area in the US and UK. One square mile is exactly 640 acres. The standard land unit in the US and UK — originally the area one ox team could plough in a day.
Formula
ac = mi² × 640
1 mi² = 640 ac
1 ac = 0.0015625 mi²Worked example
To convert 1 mi², multiply by 640: 1 × 640 = 640 ac.
Frequently asked questions
How many acres are in a square mile?
There are 640 acres in one square mile. To convert any amount, multiply the number of square miles by 640.
How do I convert acres back to square miles?
Divide instead of multiplying, or equivalently multiply by 0.0015625. One acre is 0.0015625 square miles.
Is this conversion exact?
Yes. Since the international agreement of 1959, the relationship between square miles and acres is defined exactly rather than measured, so the only rounding here is in how many decimal places we show.
Where is each of these units used?
Square Miles: used for land and territory area in the US and UK. One square mile is exactly 640 acres. Acres: the standard land unit in the US and UK — originally the area one ox team could plough in a day.
Sources
- NIST Special Publication 811 — Guide for the Use of the International System of Units