Acreage Calculator

How do you calculate acreage from square footage?

Dividing the square footage of a parcel by 43,560 gives its acreage, since 43,560 sq ft is what one acre holds by definition. Take a back lot of 32,670 sq ft as an example: divided by 43,560, it works out at 0.75 acre. The same arithmetic run the other way turns acres back into square feet, so the 3 acres quoted in a listing cover 130,680 sq ft of ground, which is the figure a fencing or seeding quote gets built on.

A tape marked in metres adds one step, because a square metre holds 10.7639 sq ft. Take a field measured at 5,000 m² as an example: converted, it comes to 53,819.55 sq ft, which divided by 43,560 lands on 1.2355 acres.

A deed quoting 1 acre tells a contractor pricing by the square foot very little, which is why a square footage acreage calculator keeps four units on screen together, the same 0.75 acre reading as 32,670 sq ft, 3,035.14 m² and 0.3035 hectare.

How big is an acre?

One acre covers 43,560 sq ft, which laid out as a square runs 208.71 ft on each side. An acre measures surface and says nothing about shape, so the same 43,560 sq ft stretched into a ribbon 40 ft wide runs 1,089 ft deep.

The odd number 43,560 is a leftover from medieval ploughing. An acre was one chain by one furlong, that is 66 ft by 660 ft, the strip a team of oxen was reckoned to turn over in a day. That chain is the surveyor's chain standardised by Edmund Gunter around 1620, the same 22 yards that still separate the wickets on a cricket pitch.

An American football field between the goal lines measures 300 by 160 ft for a total of 48,000 sq ft, which puts one acre at about 91% of the rectangle. Holdings measured in hundreds of acres get counted by the section instead. One section is a square mile of 640 acres.

How many acres is a typical lot?

A listing that reads 0.25 acre is describing about 10,890 sq ft of ground, which in a typical subdivision comes out near 99 by 110 ft. The same handful of sizes repeats from one development to the next, each row below divided by 43,560 and converted at the exact factor 1 sq ft = 0.09290304 m².

That quarter-acre row is the one worth carrying in the head, since a listing that says quarter acre is promising 10,890 sq ft of ground. An infill parcel squeezed into a built-up street often stops near 5,000 sq ft, which works out at 0.1148 acre.

Both figures describe open ground, driveway and setbacks included. Floor area is a separate measurement that belongs in the square footage calculator, which adds up finished rooms one at a time, while acreage stays outside the walls.

How to calculate acreage of an irregular lot

Averaging each pair of opposite sides and multiplying the two averages gives the area of a four-sided lot, which divided by 43,560 gives the acreage. The four-sided mode applies that trapezoid method, pairing side A with side C and side B with side D once the boundary has been walked in order. Four side lengths never pin down a single shape, so the answer comes back flagged as an estimate.

Take sides of 210, 190, 230 and 205 ft as an example: the opposite pairs average 220 ft and 197.5 ft. Multiplied together they give 43,450 sq ft, which the calculator reads as 0.9975 acre with an estimate badge beside it. Those four lengths often come off a plat map or a deed instead of a tape.

That approximation is exact on a rectangle or a parallelogram. It drifts by a few percent as soon as the corners skew away from 90 degrees, further still on a lot with five or six sides, so an angular parcel is better handled by splitting the outline into triangles measured from a single fixed corner.

An estimate is enough for ordering fence posts or working out how much seed a field will take. Anything with legal weight behind it, a deed, a sale, a permit application, calls for a boundary survey signed by a licensed surveyor, whose figure comes from measured angles and coordinates instead of averaged sides.