Square Miles to Acres Converter
Convert square miles to acres — exactly 640 acres to the square mile. Results update as you type; exact factors shown.
One square mile is 640 acres — see the exact factor, not a rounded rule of thumb.
How the square miles to acres converter works
Areas convert through the square metre. Because the inch is exactly 25.4 mm, a square foot is exactly 0.09290304 m², an acre (43,560 square feet) is exactly 4,046.8564224 m² and a square mile (640 acres) is 2,589,988.110336 m². A hectare is 10,000 m² by definition.
The UK is metric for most trade and science but keeps miles, pints, stone and mpg (with the imperial gallon) in daily life.
Common area conversions
| From | To | Units |
|---|---|---|
| 0.01 mi² | 6.4 ac | square miles to acres |
| 0.1 mi² | 64 ac | square miles to acres |
| 0.25 mi² | 160 ac | square miles to acres |
| 0.5 mi² | 320 ac | square miles to acres |
| 1 mi² | 640 ac | square mile to acres |
| 2 mi² | 1,280 ac | square miles to acres |
| 5 mi² | 3,200 ac | square miles to acres |
| 10 mi² | 6,400 ac | square miles to acres |
| 25 mi² | 16,000 ac | square miles to acres |
| 50 mi² | 32,000 ac | square miles to acres |
| 100 mi² | 64,000 ac | square miles to acres |
| 1,000 mi² | 640,000 ac | square miles to acres |
Units in this converter and their exact factors
| Unit | Symbol | One unit in square metres |
|---|---|---|
| square millimetre | mm² | 0.000001 square metre |
| square centimetre | cm² | 0.0001 square metre |
| square metre | m² | 1 square metre |
| hectare | ha | 10,000 square metre |
| square kilometre | km² | 1,000,000 square metre |
| square inch | in² | 0.00064516 square metre |
| square foot | ft² | 0.09290304 square metre |
| square yard | yd² | 0.83612736 square metre |
| acre | ac | 4,046.8564224 square metre |
| square mile | mi² | 2,589,988.110336 square metre |
FAQFrequently asked questions about area conversion
How many acres in a square mile?
Exactly 640.
Why 640?
Because an acre is one furlong by one chain, and a square mile divides into 640 of them — a number chosen to quarter neatly.
What is a section?
One square mile, 640 acres, in the US Public Land Survey.
What is a quarter section?
160 acres, the standard homestead grant.
What is 1 mi² in km²?
2.59 km².
Where these figures come from
- BIPM — The International System of Units (SI Brochure, 9th edition) — definitions of the base and derived units.
- NIST Special Publication 811 — Guide for the Use of the International System of Units — the exact conversion factors used here.
- National Physical Laboratory (NPL) — United Kingdom's national measurement authority.
Last checked: September 2026. Conversion factors are fixed by definition and do not change with tax years or regulations.