Square Miles to Acres
Convert square miles to acres instantly. 1 mi² = 640 ac. Includes the exact factor, a conversion table of common values and the definition of both units.
How to convert square miles to acres
To convert square miles to acres, multiply by 640. The relationship is fixed, so the same factor works for any quantity — there is nothing to look up and nothing that changes with temperature, location or context.
ac = mi² × 640
Square Miles to Acres conversion table
The values people look up most often, rounded for reading. Use the calculator above for anything in between.
| Square Miles | Acres |
|---|---|
| 1 mi² | 640 ac |
| 2 mi² | 1,280 ac |
| 3 mi² | 1,920 ac |
| 5 mi² | 3,200 ac |
| 10 mi² | 6,400 ac |
| 20 mi² | 12,800 ac |
| 25 mi² | 16,000 ac |
| 50 mi² | 32,000 ac |
| 100 mi² | 64,000 ac |
| 500 mi² | 320,000 ac |
| 1,000 mi² | 640,000 ac |
What is a square mile?
640 acres. Used for counties, states and weather-warning areas.
What is a acre?
43,560 square feet — historically the area one ox team could plough in a day.
The formula
ac = mi² × 640
Every result on this page comes from this formula. Nothing is rounded until the final display, so figures match a spreadsheet to the cent.
How to use the Square Miles to Acres
- Type the number of square miles you want to convert.
- Read the result in acres straight away — there is no button to press.
- Check the table below for the values that come up most often, or reverse the conversion with the linked acres to square miles page.
Square Miles to Acres — frequently asked questions
How many acres are in a square mile?
One square mile equals 640 ac. ac = mi² × 640
What is the formula to convert square miles to acres?
The formula is ac = mi² × 640. It is an exact definition rather than an approximation, so the conversion never drifts no matter how large the number.
How do I convert acres back to square miles?
Divide instead of multiplying: one acre is 0.0015625 mi². The reverse converter is linked in the related tools list.
Is this conversion exact?
Yes. Both units are defined against the same base unit by international agreement, so the factor is exact — any rounding you see is only in the display, which you can widen by entering more decimal places.
Is this square miles to acres free to use?
Yes. Every calculator on the site is free, needs no sign-up, and runs entirely in your browser, so your figures never leave your device.
What people search for
This page answers each of these searches. They are the exact phrases visitors use to find the square miles to acres.
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About this calculator
Written and reviewed by The Samsung Calculator editorial team. Every calculator is written against a published formula, reviewed against at least one independent reference implementation, and dated when it changes.
Last reviewed August 15, 2026 · Calculation runs client-side · No data collected · Report an error