Convert Square Mile to Acre (mi² → ac)

Converting square miles to acres is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.

1. 1
   Take your value in square miles

   Start with the number of square miles (mi²) you want to convert.
2. 2
   Multiply by 640

   The conversion factor from mi² to ac is 640. Multiply your value by this number.
3. 3
   Read the result in acres

   The result is your value in acres (ac).

Multiply the value in square miles by 640. For the reverse direction, multiply by 0.001563.

• ✓1 mi² = 2.59 km² = 640 acres.
• ✓US land survey "section" = 1 mi²; "township" = 36 mi².
• ✓Common in US geography; replaced by km² in most of world.

• ✗Confusing square miles with statute miles (length).
• ✗Using 2.5 km² shortcut — correct 2.59 km² differs by 3.5%.
• ✗Mixing nautical square miles (irregular) with statute square miles.

What is the Square Mile?

The square mile equals exactly 2.589988110336 square kilometers (or 640 acres) and is the American unit for measuring large geographic areas: counties, states, watersheds, and large parks. The continental United States covers about 3 million square miles, and Texas alone is 268,597 mi². Population density in US contexts is given in people per square mile (e.g., New York City has about 27,000 people/mi²). The square mile relates to the acre (640 acres = 1 mi²), the square kilometer (1 mi² ≈ 2.59 km²), the square foot (1 mi² = 27,878,400 ft²), and the hectare (1 mi² ≈ 259 ha). It is the natural large-area unit for American geographic discussion, though metric countries use square kilometers for the same purpose.

• US states, counties and cities
• UK geographic and historical boundaries
• Large estate and national-park reporting in Anglo contexts

What is the Acre?

The acre equals exactly 4,046.8564224 square meters (or 43,560 square feet) and is the standard unit for American and British farmland, real estate, and recreational property. The unit's origin is medieval: an acre was the area a yoke of oxen could plow in one day, traditionally a strip 1 furlong (660 ft) by 1 chain (66 ft). Despite metric adoption in many fields, the acre persists in property records throughout the US and UK. A standard American football field (excluding end zones) is about 1.32 acres. The largest US state, Alaska, contains about 365 million acres. The acre relates to the square foot (43,560 ft² = 1 acre), the hectare (1 ha ≈ 2.471 acres), the square mile (640 acres = 1 mi²), and the square meter (1 acre ≈ 4,047 m²). US farms average around 446 acres, and the average UK farm is about 215 acres.

• US farmland and ranches
• UK rural property and estates
• Canadian rural property (legal survey system)