Convert Acres to Square Miles
Acres to square miles is the conversion you need when land runs large — big farms, ranches, or survey tracts — and acres stop being easy to picture. One acre is exactly 0.0015625 square miles, which is exactly one 640th, so the number gets much smaller when you switch from acres to square miles.
Acres to Square miles conversion table
| Acres (ac) | Square miles (mi²) |
|---|---|
| 1 | 0.001563 |
| 2 | 0.003125 |
| 3 | 0.004688 |
| 5 | 0.007813 |
| 10 | 0.015625 |
| 20 | 0.03125 |
| 50 | 0.078125 |
| 100 | 0.15625 |
| 500 | 0.78125 |
| 1,000 | 1.5625 |
The formula
To convert acres to square miles, multiply the number of acres by 0.0015625 (which is exactly 1/640):
square miles = acres × 0.0015625
A worked example
Say you have 320 acres — half of a survey section — and want it in square miles:
320 × 0.0015625 = 0.5 mi²
So 320 acres is exactly half a square mile.
Why the number is exact
The acre and the square mile are both defined from the same unit — the foot — so they line up cleanly. There are exactly 640 acres in one square mile, which is why a square mile is called a "section" in the US Public Land Survey System. That makes one acre exactly 1/640 of a square mile, or 0.0015625 — an exact fraction, not an approximation.
When you'll use it
Measuring large tracts like farms, ranches, and forests, reading US survey sections and townships, and comparing land parcels that are too big to picture comfortably in acres.
Frequently asked questions
How many acres are in a square mile?
Exactly 640 acres. That's why a square mile is called a 'section' in the US land survey system — it's a fixed, exact number, not a rounded one.
How many square miles are in an acre?
Exactly 0.0015625 square miles, which is exactly 1/640. Since there are 640 acres in a square mile, one acre is one 640th of a square mile.
Is the acres to square miles conversion exact?
Yes. There are exactly 640 acres in a square mile, so an acre is exactly 1/640 of a square mile — 0.0015625 — with nothing rounded away.