Acres to Square Miles Converter
Convert acres to square miles — divide by 640. Results update as you type; exact factors shown.
One acre is 0.0016 square miles — see the exact factor, not a rounded rule of thumb.
How the acres to square miles converter works
Areas convert through the square meter. 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 US uses customary units (US gallon, short ton, °F) in daily life; NIST SP 811 gives the exact SI factors.
Common area conversions
| From | To | Units |
|---|---|---|
| 40 ac | 0.0625 mi² | acres to square miles |
| 80 ac | 0.125 mi² | acres to square miles |
| 160 ac | 0.25 mi² | acres to square miles |
| 320 ac | 0.5 mi² | acres to square miles |
| 640 ac | 1 mi² | acres to square miles |
| 1,280 ac | 2 mi² | acres to square miles |
| 2,560 ac | 4 mi² | acres to square miles |
| 5,000 ac | 7.8125 mi² | acres to square miles |
| 10,000 ac | 15.625 mi² | acres to square miles |
| 25,000 ac | 39.0625 mi² | acres to square miles |
| 50,000 ac | 78.125 mi² | acres to square miles |
| 100,000 ac | 156.25 mi² | acres to square miles |
Units in this converter and their exact factors
| Unit | Symbol | One unit in square meters |
|---|---|---|
| square millimeter | mm² | 0.000001 square meter |
| square centimeter | cm² | 0.0001 square meter |
| square meter | m² | 1 square meter |
| hectare | ha | 10,000 square meter |
| square kilometer | km² | 1,000,000 square meter |
| square inch | in² | 0.00064516 square meter |
| square foot | ft² | 0.09290304 square meter |
| square yard | yd² | 0.83612736 square meter |
| acre | ac | 4,046.8564224 square meter |
| square mile | mi² | 2,589,988.110336 square meter |
FAQFrequently asked questions about area conversion
How many acres in a square mile?
640.
What is 160 acres?
A quarter section — 0.25 square miles.
What is 40 acres?
A quarter of a quarter section, 0.0625 mi². The phrase "forty acres" comes from this subdivision.
What is an acre in square meters?
4,046.86 m².
How large is a typical US farm?
The average is around 450 acres, or 0.7 square miles, though the distribution is extremely skewed.
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 Institute of Standards and Technology (NIST) — United States's national measurement authority.
Last checked: September 2026. Conversion factors are fixed by definition and do not change with tax years or regulations.