Convert Square Mile to Acre
Convert square miles to acres instantly. 1 square mile = 640 acre — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Acre to Square Mile converter for the reverse conversion.
Units explained
Square Mile
A square mile is an imperial unit of area equal to exactly 2,589,988.110336 m². It is used for measuring large land areas in the United States and the United Kingdom.
Derived by squaring the statute mile (5,280 feet). The mile was standardized via the 1959 International Yard and Pound Agreement.
Square miles are used for US and UK regional geography (county areas, lake sizes, large parks), national statistics, and military range descriptions. 1 mi² = 640 acres = 2.589988 km².
Mile dates to Roman antiquity; modern exact value standardized in 1959.
Acre
An acre is an imperial unit of area equal to exactly 4046.8564224 m². It is the most widely used non-metric unit for land area, particularly in the US, UK, and India.
Originally defined in medieval England as the area one yoke of oxen could plow in a day, approximately 40 perches by 4 perches. Standardized via the 1959 International Yard and Pound Agreement.
Acres are the standard land measurement unit in the US (real estate, agriculture), the UK (rural property), and widely used in India (alongside hectares and traditional regional units). 1 acre = 4840 sq yd = 43,560 sq ft = 0.4047 hectare.
Medieval English farming origin; modern exact value standardized in 1959.
Square Mile to Acre conversion formula
The relationship between square miles and acres:
To convert square miles to acres, multiply the value in square miles by 640. To reverse, multiply acres by 0.0015625.
How to use this converter
Type a value into the calculator. The result in acres updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Acre to Square Mile converter for the reverse direction.
Step-by-step: convert square miles to acres
- Write down the value in square miles (mi²).
- Multiply that value by the factor 640.
- The product is the equivalent value in acres (ac).
- To reverse, multiply the acre value by 0.0015625.
Worked examples
Example 1 — Convert 1 mi² to ac:
1 × 640 = 640 ac
Example 2 — Convert 100 mi² to ac:
100 × 640 = 64000 ac
Square Mile to Acre conversion table
Standard reference values for converting square miles to acres:
| Square Mile [mi²] | Acre [ac] |
|---|---|
| 0.01 | 6.4 |
| 0.1 | 64 |
| 1 | 640 |
| 2 | 1280 |
| 3 | 1920 |
| 4 | 2560 |
| 5 | 3200 |
| 10 | 6400 |
| 20 | 12800 |
| 30 | 19200 |
| 40 | 25600 |
| 50 | 32000 |
| 100 | 64000 |
| 500 | 320000 |
| 1000 | 640000 |
Frequently asked questions
How many acres is 1 square mile?
How do I convert square miles to acres?
How do I convert acres back to square miles?
How many acres is 100 square miles?
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Metric / SI (5 units)
Imperial / US Customary (14 units)
Sources & references
Conversion factor (1 mi² = 640 ac) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- NIST — Refinement of values for the yard and pound (Federal Register 1959)
The treaty (signed by US
- International Hydrographic Organization — Resolution on the Nautical Mile
International authority that standardised the nautical mile at exactly 1852 m in 1929 — the value adopted worldwide for sea and air navigation.