How many square feet are in an acre?
Exactly 43,560. To turn acres into square feet, multiply by 43,560; to turn square feet into acres, divide by 43,560. A quarter acre is 10,890 square feet, a third of an acre 14,520 and half an acre 21,780. The other way round, 5,000 square feet is 0.1148 acres and 10,000 square feet is 0.2296.
Land in the United States is recorded in acres, but lots smaller than an acre are often listed in square feet, so the conversion is the quick sanity check: a 9,000 square foot lot is 0.21 acres, a normal suburban plot rather than an estate.
Why 43,560?
Because the acre is older than the foot it is now measured in. It was a day’s ploughing, fixed as a furlong (660 feet) by a chain (66 feet), and 660 × 66 is 43,560. The same arithmetic makes 10 acres a square exactly 660 feet on a side, and 640 acres a square mile.
What an acre looks like
As a square, an acre is about 208.7 feet on each side and a quarter acre about 104.4 feet. Lots are rarely square, though, and a long, narrow lot needs more fence than a square of the same area. When a listing gives the frontage, the depth follows: divide the square feet by the frontage, as the lot tool above does. For an acre drawn beside a football field, tennis courts and a square mile, see how big is an acre.
Is every acre the same size?
For anything bought today, yes. Since 1 January 2023 the US survey foot has been deprecated in favour of the international foot of exactly 0.3048 metres; the survey acre was larger by only about 25 square inches, a difference that matters on old surveys and nowhere else. Some sellers speak of a “commercial acre” of 36,000 square feet or a “builder’s acre” of 40,000. Neither appears in NIST Handbook 44 — they are sales conventions — so check the square feet written on the deed.
Measure your own land
Do not know the acreage yet? The acreage calculator measures a plot drawn on a satellite map, on the Earth’s own shape. A flat web map overstates area by about 70% at 40° north, the latitude of Philadelphia and Denver, and by more further north; the calculator brings its answer back here.