An international acre is 4,046.8564224 square meters.
Acres to Square miles Converter — ac to mi2
Convert Acre (ac) to Square mile (mi2) using the exact conversion factor (1 acre = 0.0015625 square mile). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Acres to Square miles converter
Converter
Agriculture Converter
Convert acres, hectares, yield, seed, fertilizer, irrigation, and application-rate units.
Context values
Some unit families need one extra value for a physically accurate result.
A square mile is 640 acres.
Result = input x 4046.856422 / 2.58998811e+6.
Area units are compatible.
Reserved above the conversion cards and below the converter.
About Converting Acres to Square miles
Acre and Square mile both measure a farming-related quantity — a land area or an application/yield rate per unit area — used to report crop yields, calculate how much fertilizer or seed a field needs, and plan irrigation. Acre is typically associated with united States, while Square mile is typically associated with united States (county, metro, and regional area reporting).
Formula
square miles = acres × 0.0015625
This factor comes from each unit's defined relationship to the category's base unit: 1 acre equals 4046.8564224 base units, and 1 square mile equals 2589988.11034 base units, so dividing one by the other gives the direct acre-to-square mile factor of 0.0015625.
Simple example
1 ac × 0.0015625 = 0.0015625 mi2
1 acre = 0.0015625 square miles.
Real-world example
100 ac × 0.0015625 = 0.15625 mi2
100 acres = 0.15625 square miles.
Conversion table
| Acre (ac) | Square mile (mi2) |
|---|---|
| 1 ac | 0.0015625 mi2 |
| 5 ac | 0.0078125 mi2 |
| 10 ac | 0.015625 mi2 |
| 50 ac | 0.078125 mi2 |
| 100 ac | 0.15625 mi2 |
| 500 ac | 0.78125 mi2 |
Reverse conversion: Square mile to Acre
0.0015625 mi2 × 640 = 1 ac
0.0015625 square miles = 1 acre.
acres = square miles × 640
For a page dedicated to this direction, see Square mile to Acre.
Acre vs. Square mile
| Aspect | Acre | Square mile |
|---|---|---|
| Family | US/imperial customary unit | US/imperial customary unit |
| Typical use | Measuring farmland, ranch, and rural property size in the US | US city, county, and regional area statistics |
| Where it's used | United States | United States (county, metro, and regional area reporting) |
Understanding the Acre
Acre (ac) measures area. The international acre is defined as exactly 4,046.8564224 square meters. It is classified as a US/imperial customary unit.
Where it's used: United States United Kingdom (informal/historical, land registry legacy) Countries with historical British land-survey systems
International acre vs. US survey acre. The US survey acre, based on the US survey foot, differs from the international acre by about two parts per million. The US retired the survey foot/acre for federal use at the end of 2022.
Uses of the Acre today
- Measuring farmland, ranch, and rural property size in the US
- Real estate listings and zoning for land parcels
- Forestry and land-management reporting
History of the Acre
The acre originated in medieval England as a practical field measurement: the area a yoke of oxen could plow in one day, roughly a furlong (660 ft) long by a chain (66 ft) wide, giving the 43,560 square feet still used today.
Edward I's 1305 statute formalized this figure. In 1959, the same International Yard and Pound Agreement that fixed the pound also fixed the international acre at exactly 4,046.8564224 m², though the US separately retained a slightly different 'US survey acre' for some legacy land records until it was phased out in 2023.
Historical origin. Acre was not the invention of a single named person; it developed through the process described above.
Understanding the Square mile
Square mile (mi2) measures area. A square mile is exactly 2,589,988.110336 square meters, derived from the international mile fixed in 1959. It is classified as a US/imperial customary unit.
Where it's used: United States (county, metro, and regional area reporting)
Uses of the Square mile today
- US city, county, and regional area statistics
- Population density reporting (people per square mile)
- Land-use and geography in US contexts
History of the Square mile
The square mile follows directly from the statute mile, itself fixed at exactly 1,609.344 meters by the 1959 International Yard and Pound Agreement; squaring that value gives the modern square mile.
Historical origin. Square mile was not the invention of a single named person; it developed through the process described above.
Acre — sources
- NIST — US Survey Foot: Revised Unit Conversion Factors — Documents the 1959 international acre definition and the 2022/2023 survey-foot retirement.
Square mile — sources
- NIST — International yard and pound (1959) — Basis for the modern mile and its derived area unit.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many square miles are in 1 acre?
1 acre equals 0.0015625 square miles, using the exact defined conversion factor rather than an estimate.
How do I convert acre to square mile?
Multiply the acre value by 0.0015625. The converter above does this instantly to whatever precision you set.
How do I convert square mile back to acre?
Use the reverse factor: 1 square mile equals 640 acres. You can also use the swap control in the converter above to flip the direction instantly.
What is a acre?
Acre (ac) measures area. The international acre is defined as exactly 4,046.8564224 square meters. It is classified as a US/imperial customary unit.
What is a square mile?
Square mile (mi2) measures area. A square mile is exactly 2,589,988.110336 square meters, derived from the international mile fixed in 1959. It is classified as a US/imperial customary unit.
Is the acre to square mile conversion exact?
Yes. A square mile is exactly 2,589,988.110336 square meters, derived from the international mile fixed in 1959. That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.
What is the difference between international acre vs. us survey acre?
The US survey acre, based on the US survey foot, differs from the international acre by about two parts per million. The US retired the survey foot/acre for federal use at the end of 2022.
Where is the acre still used today?
United States United Kingdom (informal/historical, land registry legacy) Countries with historical British land-survey systems