Square Miles to Acres (mi² to ac) Converter
1 square mile equals exactly 640 acres — multiply the number of square miles by 640 to convert. So 5 mi² is 3,200 acres and 10 mi² is 6,400 acres.
The formula
To convert square miles to acres, multiply by 640:
acres = square miles × 640
For example, 2.5 mi² × 640 = 1,600 ac. This is a clean, exact relationship — a square mile is defined as 640 acres, and one section of US public land survey equals exactly 1 mi². To reverse it, divide acres by 640.
Conversion table
| Square miles (mi²) | Acres (ac) |
|---|---|
| 1 | 640 |
| 2 | 1,280 |
| 5 | 3,200 |
| 10 | 6,400 |
| 25 | 16,000 |
| 50 | 32,000 |
| 100 | 64,000 |
| 500 | 320,000 |
| 1000 | 640,000 |
How to convert online
Live and instant:
- Type the number of square miles into the first box.
- Read the acre value instantly in the second box.
- Or enter an acre value to convert back — it works both ways.
Use the Square Mile to Acre Converter — free and instant in your browser.
Where this conversion is used
Both units are imperial and central to US land measurement. Square miles describe counties, ranches and survey sections, while acres are used for individual parcels and farmland. Converting mi² to acres is routine in real estate, agriculture and land-title work.
FAQ
How many acres are in a square mile?
One square mile equals exactly 640 acres. Multiply mi² by 640 — 10 mi² = 6,400 acres.
What is the formula to convert square miles to acres?
Acres = mi² × 640. The converter applies this exact factor automatically.
How do I convert acres back to square miles?
Divide the acre value by 640, or multiply by 0.0015625. So 3,200 acres = 5 mi².
Is the conversion exact?
Yes — 640 is a definitional factor, so there is no rounding error.
Related converters
- Acre to Square Mile Converter
- Square Mile to Square Kilometer Converter
- Square Mile to Square Meter Converter
- Square Mile to Hectare Converter
Built by ByteVancer
ByteTools is a free product of ByteVancer, a software and web development studio. Every tool runs entirely in your browser — no uploads, no sign-up. Need a custom web app or tool? ByteVancer can build it.
Recommended reading
Acre to Square Mile Converter (ac to mi²)
1 acre equals 0.0015625 square miles. Use the exact factor, formula and reference table to convert acres to square miles fast.
Square Yards to Square Miles (yd² to mi²) Converter
1 square yard equals 3.228306e-7 square miles. Get the exact formula, a conversion table, and convert yd² to mi² instantly online.
Square Yards to Square Meters (yd² to m²) Converter
1 square yard equals 0.83612736 square meters. Get the exact formula, a conversion table, and convert yd² to m² instantly online.
Square Yards to Square Kilometers (yd² to km²)
1 square yard equals 8.361274e-7 square kilometers. Get the exact formula, a conversion table, and convert yd² to km² instantly online.