Acre to Square Mile Converter
Convert acres to square miles and square miles to acres instantly with the exact 640:1 land-area factor — free, private, and built for farms, real estate, and maps.
Reviewed October 7, 2026 Runs in your browser — inputs are never stored
Area Conversion
Acres ↔ square miles (exact 640:1)
Accepts decimals and large values. Conversion uses the exact factor 640 acres = 1 square mile.
500 acres = 0.78125 square miles
Quick acre to square mile conversion table
| Acres | Square miles (mi²) |
|---|---|
| 1 | 0.0015625 |
| 5 | 0.0078125 |
| 10 | 0.015625 |
| 25 | 0.0390625 |
| 50 | 0.078125 |
| 100 | 0.15625 |
| 200 | 0.3125 |
| 320 | 0.5 |
| 400 | 0.625 |
| 500 | 0.78125 |
| 640 | 1 |
| 1,000 | 1.5625 |
| 2,000 | 3.125 |
| 5,000 | 7.8125 |
| 10,000 | 15.625 |
Want formulas, worked examples, and when to use each unit? Read the Acre to Square Mile Converter guide — plus reverse conversion and common mistakes to avoid.
This tool provides general unit conversions for everyday and educational use. For regulated, legal, or scientific applications, verify conversion factors against the applicable official standard.
About the Acre to Square Mile Converter
An Acre to Square Mile Converter turns large land measurements between two customary area units used across US property records, agriculture, and geography. One square mile contains exactly 640 acres, so converting acres to square miles means dividing by 640, and converting square miles to acres means multiplying by 640. The tool is aimed at landowners comparing tracts, farmers totaling fields, students learning US customary area, surveyors cross-checking plats, and anyone reading maps or census land figures. Enter a value in acres or square miles, choose the target unit, and read a precise result with a live reference table. Results stay in your browser — nothing is stored — and the math uses the exact statutory relationship rather than a rounded approximation, so 640 acres always equals 1 mi² and 500 acres equals 0.78125 mi².
How to use it
- 1Enter the amount in acres.
- 2The equivalent in square miles appears instantly.
- 3Press the ⇌ button to convert from square miles back to acres.
- 4Choose how many decimal places to show if you need more or less precision.
Worked example
500 acres ÷ 640 = 0.78125 square miles, and 2.5 square miles × 640 = 1,600 acres.
How it works
How the Acre to Square Mile Converter works
By definition in the US customary system, 1 square mile = 640 acres. That single exact ratio drives every conversion on this page.
Formulas
Square miles = acres ÷ 640
Acres = square miles × 640
Also remember: 1 acre = 43,560 ft² ≈ 4,046.856 m², and 1 mi² = 27,878,400 ft² ≈ 2.58999 km².
Worked example
Convert 500 acres to square miles: 500 ÷ 640 = 0.78125 mi². Convert 2 mi² to acres: 2 × 640 = 1,280 acres.
When to use each unit
- Acres — parcels, farms, ranches, real-estate listings, and development tracts.
- Square miles — cities, counties, forests, lakes, and large geographic regions.
Related tools
- Area Converter — m², ft², acres, hectares, and more
- Unit Converter — multi-category unit conversion
- Area Calculator — area from shape dimensions
- Full conversion guide — tables, FAQs, and applications
Who it is for
Landowners, farmers, real-estate professionals, students, surveyors, and anyone converting large land areas between acres and square miles.
Why it helps
Manual division or multiplication by 640 is easy to reverse by mistake on large numbers; the converter applies the exact factor, supports decimals and large values, and shows a reference table for quick checks.
Common use cases
- Describing the size of a ranch or estate
- Comparing park or reserve areas
- Converting land records between units
Tips for better results
- Remember 640 acres = 1 mi² — the easiest landmark value on any land map.
- Use acres for individual parcels and square miles for cities or counties so numbers stay readable.
- Keep full precision until the final step; round only the result you report.
- Pair this tool with the Area Converter when you also need hectares, m², or ft².
Common mistakes to avoid
- Multiplying acres by 640 instead of dividing when going to square miles.
- Confusing linear miles (distance) with square miles (area).
- Writing “mi” instead of “mi²” on the result.
- Treating acres as square feet — 1 acre is already 43,560 ft².
Frequently asked questions
A:Exactly 640 acres. This is the standard US customary definition used in land measurement and mapping.
A:One acre equals 1/640 square mile, which is exactly 0.0015625 mi².
A:Divide acres by 640. Formula: square miles = acres ÷ 640. Example: 320 ÷ 640 = 0.5 mi².
A:Multiply square miles by 640. Formula: acres = square miles × 640. Example: 5 × 640 = 3,200 acres.
A:No. A square mile is much larger — it contains 640 acres. Use square miles for very large regions and acres for parcels and farms.
A:The international acre used today is 43,560 square feet. Historical or local land units can differ, so always confirm the standard used in legal or survey documents.
Reviewed for accuracy · Last updated October 7, 2026
Conversion factors are based on internationally defined SI units and standard metric/imperial equivalence tables.
CalcWisee Editorial Team
Calculator development and formula review
CalcWisee is an independent site founded by Ayman. Every calculator is built from a published formula or official definition, tested against hand-worked examples before it goes live, and corrected promptly when a reader reports an issue to ayman@calcwisee.com.
Expertise: Financial mathematics, Health and fitness formulas, Applied mathematics, Unit conversion standards
References & sources
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