Convert Square miles to Acres
1 square mile is 640 ac. One square mile is exactly 640 acres.
One square mile is 640 acres. To convert square miles to acres, multiply by 640; to go the other way, divide by 640 or multiply by 0.0015625. The factor is exact rather than rounded: it follows from NIST Office of Weights and Measures. Exactly 640 acres — one section of the US Public Land Survey, the grid the Midwest is drawn on.
Factor checked against the defining standard · How we check
- Square miles × 640
1 * 640640 ac
1 square mile in every area unit
| Unit | Value | Exact factor |
|---|---|---|
| square inches | 4,014,489,600 sq in | × 4,014,489,600 |
| square feet | 27,878,400 sq ft | × 27,878,400 |
| square yards | 3,097,600 sq yd | × 3,097,600 |
| acres | 640 ac | × 640 |
| square meters | 2,589,988.11 m² | × 2,589,988.11034 |
| square millimetres | 2,589,988,110,000 mm² | × 2,589,988,110,340 |
| square centimetres | 25,899,881,100 cm² | × 25,899,881,103.4 |
| square kilometres | 2.58998811 km² | × 2.58998811034 |
| square miles (as entered) | 1 mi² | — |
| hectares | 258.998811 ha | × 258.998811034 |
Factors are entered by hand from NIST Office of Weights and Measures rather than derived from a units library, so the ones that terminate are exact rather than rounded.
The same converter answers this pair however it is written: sqmi to ac is how the symbols are typed on a keyboard with no superscript on it.
How do you convert square miles to acres? The converter and the working
- 1.Take the measurement in square miles.
- 2.Multiply by 640 — that is how many acres fit in one square mile.
- 3.To go back the other way, divide by 640, or multiply by 0.0015625.
Worked example: 25 square miles to acres
- Formula
- mi² × 640 = ac
- Arithmetic
- 25 × 640 = 16,000 ac
- Answer
- 25 mi² = 16,000 ac
The factor is exact, so this figure is exact too — only the display is rounded.
Square miles to acres conversion table
| Square miles | Acres |
|---|---|
| 1 mi² | 640 ac |
| 2 mi² | 1,280 ac |
| 3 mi² | 1,920 ac |
| 4 mi² | 2,560 ac |
| 5 mi² | 3,200 ac |
| 6 mi² | 3,840 ac |
| 7 mi² | 4,480 ac |
| 8 mi² | 5,120 ac |
| 9 mi² | 5,760 ac |
| 10 mi² | 6,400 ac |
| 12 mi² | 7,680 ac |
| 15 mi² | 9,600 ac |
| 20 mi² | 12,800 ac |
| 25 mi² | 16,000 ac |
| 50 mi² | 32,000 ac |
| 100 mi² | 64,000 ac |
| 200 mi² | 128,000 ac |
| 300 mi² | 192,000 ac |
| 500 mi² | 320,000 ac |
| 1000 mi² | 640,000 ac |
| 2000 mi² | 1,280,000 ac |
| 5000 mi² | 3,200,000 ac |
| 10000 mi² | 6,400,000 ac |
640 acres to the square mile, and that is by design
The US Public Land Survey divided the country into townships of 36 square miles, each square mile a section of 640 acres, each quarter-section 160 acres — the homestead. The number is round because the survey chose it, unlike the 43,560 square feet in an acre, which is inherited from a chain by a furlong. That is why rural addresses reference sections and why farm parcels come in halves and quarters of 160.
NIST Handbook 44, Appendix C — general tables of units of measurement
What is a square mile?
Exactly 640 acres — one section of the US Public Land Survey, the grid the Midwest is drawn on. 2.59 square kilometres, and the reason a rural address is often "section 12".
What is an acre?
Exactly 43,560 square feet — historically the land one team of oxen could plough in a day.
How many acres are in a square mile?
One square mile is 640 acres, exactly. Going the other way, one acre is 0.0015625 square miles. Both figures come from the same defined relation rather than from a measurement, which is why they are the same today as they were in 1959.
Every area unit here
The whole group — 10 units with their symbols and the size of each one in square meters — is on the conversion index, along with every pair it makes. The table above already gives each of them relative to a square mile.
Cite this page
- APA
- Rule Calculator. (2026). Convert Square miles to acres. Rule Calculator. https://rulecalculators.com/convert/square-mile-to-acre
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- Chicago
- Rule Calculator. "Convert Square miles to acres." Rule Calculator. Last reviewed August 16, 2026. https://rulecalculators.com/convert/square-mile-to-acre.
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Questions people actually ask
- How many acres are in a square mile?
- 640. Exactly 43,560 square feet — historically the land one team of oxen could plough in a day.
- How do I convert acres back to square miles?
- Divide by 640, or multiply by 0.0015625 — they are the same operation.
Other area conversions
Acres to square miles — the same conversion the other way.