Convert Acre to Square Mile
Convert acres to square miles instantly. 1 acre = 0.0015625 square mile — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Square Mile to Acre converter for the reverse conversion.
Units explained
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
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 to Square Mile conversion formula
The relationship between acres and square miles:
To convert acres to square miles, multiply the value in acres by 0.0015625. To reverse, multiply square miles by 640.
How to use this converter
Type a value into the calculator. The result in square miles updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Square Mile to Acre converter for the reverse direction.
Step-by-step: convert acres to square miles
- Write down the value in acres (ac).
- Multiply that value by the factor 0.0015625.
- The product is the equivalent value in square miles (mi²).
- To reverse, multiply the square mile value by 640.
Worked examples
Example 1 — Convert 1 ac to mi²:
1 × 0.0015625 = 0.0015625 mi²
Example 2 — Convert 100 ac to mi²:
100 × 0.0015625 = 0.15625 mi²
Real-world example — Endurance race distances
A 50-acre cycling or running race converts to a recognizable distance in square miles. Endurance athletes coming from a different measurement system use this conversion to compare training plans across regions.
50 ac × 0.0015625 = 0.078125 mi²
Real-world example — Maritime exclusion zone
A 200-acre exclusion zone (a common maritime boundary) converts to a different value in square miles that's useful when describing the same zone in everyday land-distance units.
200 ac × 0.0015625 = 0.3125 mi²
Real-world example — Coastal cruise distances
A 10-acre coastal sailing route converts to a different value in square miles — useful for cruise operators who switch between maritime, aviation, and road-distance units depending on the leg of the trip.
10 ac × 0.0015625 = 0.015625 mi²
Acre to Square Mile conversion table
Standard reference values for converting acres to square miles:
| Acre [ac] | Square Mile [mi²] |
|---|---|
| 0.01 | 1.5625e-5 |
| 0.1 | 0.00015625 |
| 1 | 0.0015625 |
| 2 | 0.003125 |
| 3 | 0.0046875 |
| 4 | 0.00625 |
| 5 | 0.0078125 |
| 10 | 0.015625 |
| 20 | 0.03125 |
| 30 | 0.046875 |
| 40 | 0.0625 |
| 50 | 0.078125 |
| 100 | 0.15625 |
| 500 | 0.78125 |
| 1000 | 1.5625 |
Frequently asked questions
How many square miles is 1 acre?
How do I convert acres to square miles?
How do I convert square miles back to acres?
How many square miles is 100 acres?
Popular area unit conversions
Convert Acre to other area units
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Metric / SI (16 units)
Imperial / US Customary (14 units)
US Survey (5 units)
Indian Subcontinent (16 units)
Other Regional (10 units)
Scientific / Physics (5 units)
Historical / Pre-metric European (6 units)
Sources & references
Conversion factor (1 ac = 0.0015625 mi²) 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 Astronomical Union — System of Astronomical Constants
The IAU defines astronomical units including the AU (149597870700 m exactly) light-year and parsec used in astronomy and astrophysics.