An acre measures land. It is defined as 43,560 square feet, the same as 10 square chains or 160 square rods. Because the acre is a unit of area and not a shape, an acre can be a long strip or a square; a square acre would be about 208.71 ft on each side.
Formula
square feet = acres × 43,560
hectares = acres × 0.40468564
NIST lists the acre as 4,046.8564224 m² when based on the international foot, and 4,046.8726 m² on the older US survey foot. One hectare is 2.471 acres, and one square mile is 640 acres.
Example
A 2.5-acre parcel has 2.5 × 43,560 = 108,900 ft², which is 2.5 × 0.40468564 = 1.012 ha or 10,117 m².
Common mistakes
- Treating an acre as a fixed shape. Only the area is fixed.
- Mixing acres with square miles: 640 acres make one square mile, not 100 or 1,000.
See how many square feet are in an acre and the converters acres to square feet and acres to hectares.