One square mile is exactly 640 acres. Multiply square miles by 640 to get acres. In the United States this is more than a conversion factor: a square mile is the standard section of the Public Land Survey System, and many farms, ranches and legal descriptions west of the original colonies are built from sections and their fractions. Because 640 is exact, the answer needs no rounding.
Formula
Square Miles to Acres conversion table
| Square Miles | Acres |
|---|---|
| 0.25 mi² | 160 ac |
| 0.5 mi² | 320 ac |
| 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 |
| 15 mi² | 9,600 ac |
| 20 mi² | 12,800 ac |
| 25 mi² | 16,000 ac |
| 30 mi² | 19,200 ac |
| 40 mi² | 25,600 ac |
| 50 mi² | 32,000 ac |
| 60 mi² | 38,400 ac |
| 70 mi² | 44,800 ac |
| 75 mi² | 48,000 ac |
| 80 mi² | 51,200 ac |
| 90 mi² | 57,600 ac |
| 100 mi² | 64,000 ac |
| 250 mi² | 160,000 ac |
| 500 mi² | 320,000 ac |
| 1,000 mi² | 640,000 ac |
Where you’ll use it
A section of 640 acres is split into quarter sections of 160 acres, and those into quarter-quarters of 40 acres, which is where the phrase "the back forty" comes from. A township is 36 sections, or 23,040 acres. Wildfire reports, ranch listings, conservation easements and county areas move between square miles and acres all the time, so this conversion turns up in news coverage as well as in deeds.
Tip: A surveyed section is nominally 640 acres, but real ones vary. Survey corrections and the curvature of the Earth push the irregularities into sections along a township's north and west edges, which can be noticeably smaller or larger. Check the legal description, not just the section count.