Square Miles to Acres
Convert square miles (mi²) to acres (ac). Both measure surface measurement, and the conversion comes up in real estate, farming, construction work.
The Formula
``
acres = square miles × 640
square miles = acres × 0.0015625
`
One square mile is 640 acres, and one acre is 0.001563 square miles.
Conversion Table
| Square Miles | Acres |
|---|---|
| 1 mi² | 640 ac |
| 2 mi² | 1,280 ac |
| 5 mi² | 3,200 ac |
| 10 mi² | 6,400 ac |
| 25 mi² | 16,000 ac |
| 50 mi² | 32,000 ac |
| 100 mi² | 64,000 ac |
| 500 mi² | 320,000 ac |
| 1,000 mi² | 640,000 ac |
The Other Direction
| Acres | Square Miles |
|---|---|
| 1 ac | 0.001563 mi² |
| 2 ac | 0.003125 mi² |
| 5 ac | 0.007813 mi² |
| 10 ac | 0.015625 mi² |
| 25 ac | 0.039063 mi² |
| 50 ac | 0.078125 mi² |
| 100 ac | 0.15625 mi² |
| 500 ac | 0.78125 mi² |
| 1,000 ac | 1.5625 mi² |
What Each Unit Is
Square Miles (mi²) — 640 acres, or 2.589988 square kilometres. The unit of the US Public Land Survey System, which divided the west into square-mile sections.
Acres (ac) — exactly 4,046.8564224 square metres, or one furlong by one chain. The area a yoke of oxen could plough in a day — long and thin, because turning wasted time.
A Sense of Scale
A survey township is 36 square miles- San Francisco is 47 square miles
- An American football field is 1.32 acres
- A soccer pitch is about 1.8 acres
Precision
The factor 640 is exact by international agreement, not a rounded approximation. Any imprecision in a result comes from your input, not the conversion.
In Code
`javascript
const squareMileToAcre = (value) => value * 640;
``
Where This Conversion Comes Up
- Real estate
- Farming
- Construction
- Landscaping
- Flooring
How Many Decimals Do You Need?
Rounding the factor costs accuracy, and how much depends on the factor. Converting 137 mi² with the factor truncated at each decimal place:
| Decimals kept | Factor | 137 mi² becomes | Error |
|---|---|---|---|
| 0 | 640 | 87,680 | — |
| 1 | 640 | 87,680 | — |
| 2 | 640 | 87,680 | — |
| 3 | 640 | 87,680 | — |
| 4 | 640 | 87,680 | — |
The right number of significant figures is set by your input, not by the converter. If you measured square miles to three significant figures, the answer in acres is only good to three — writing more digits claims precision the measurement never had.