How big is an acre?

An acre, by the numbers

One acre is 43,560 square feet. The same area can be written a few other ways, and each is exact:

• 43,560 square feet
• 4,840 square yards
• about 4,047 square meters, or 0.405 hectares
• 1/640 of a square mile (there are 640 acres in a square mile)

The acre is an area, not a shape. A square acre measures about 208.7 feet on each side, but an acre can be long and thin, an L, or any outline at all, as long as the enclosed area comes to 43,560 square feet. That is why two acres can look nothing alike on a map and still be the same size.

An acre next to a football field

The football field is the comparison almost everyone reaches for, and it is a good one once you are precise about it. A regulation field, counting both end zones, is 360 feet by 160 feet, which is 57,600 square feet. An acre is 43,560 square feet. So an acre is a little under three-quarters of the whole field, and it is very close to the playing area between the two goal lines.

The shaded band is one acre, shaped to the field's 160-foot width. It reaches about 272 of the field's 360 feet, which is the same as saying an acre is roughly 76 percent of the entire field or about 91 percent of the green between the goal lines. The quick version to keep in your head: a football field without its two end zones is almost exactly an acre.

An acre next to a city block

City blocks are not standardized, so this comparison comes with a range rather than a single number. A compact square block near 300 by 300 feet works out to about 2 acres. Many blocks are larger, so a typical U.S. block lands somewhere between roughly 2 and 5 acres. If you are used to walking city blocks, an acre is smaller than most of them: closer to half a modest block than a whole one.

How many acres are in common parcel sizes

Once the single acre is anchored, the sizes people actually deal in get easier to picture. Each of these is exact area, whatever the shape on the ground:

• Quarter acre: 10,890 square feet, a common suburban lot, about 104 feet square.
• Half acre: 21,780 square feet, roughly 148 feet square.
• 1 acre: 43,560 square feet, about 209 feet square.
• 5 acres: 217,800 square feet, about 467 feet square, a common rural homesite or small hobby farm, close to 3.8 football fields.
• 10 acres: 435,600 square feet, about 660 feet square.
• 40 acres: the classic quarter-quarter of a survey section, about 1,320 feet square, a quarter mile on a side.
• 160 acres: a quarter section, half a mile on a side, the size of an old homestead claim.
• 640 acres: one full square mile, also called a section.

Why the exact shape matters more than the number

Two parcels can both be 10 acres and be worth and farm very differently, because acreage says nothing about drainage, soil, road frontage, or how the boundary falls. That is the gap between knowing how big a parcel is and knowing what it is. For the size question, the math on this page is all you need. For everything else, you need the land's own data, which is what a parcel read is for.

A note on precision. There are two acres in U.S. law, the international acre and the slightly different U.S. survey acre, and they differ by a hair, about 0.0004 percent. That difference never matters for a homesite or a farm field, so 43,560 square feet is the number to use.

To keep learning the land vocabulary, see how many acres are in a section for how the 640-acre grid is laid out, how to calculate acreage for the math on any shape, what a plat map is for how parcels are recorded, and how much an acre of land costs when you get to value.