How to Calculate Acreage of a Property

To calculate acreage, multiply the lot's length by its width in feet to get square feet, then divide by 43,560. One acre is 43,560 square feet, so 200 ft × 217.8 ft = 43,560 sq ft = 1 acre. Everything else on this page is a way to get the square feet when the lot isn't a tidy rectangle.

Step by Step: Rectangles and Squares

1. Measure the length and width in feet.
2. Multiply them to get square feet.
3. Divide by 43,560 to get acres.

Both measurements have to be in the same unit before you multiply. Yards, meters and chains are covered in the next section.

Going the Other Way: Acres to Dimensions

If you know the acreage and one side, divide 43,560 times the acres by that side. A 2-acre lot that's 250 feet wide is 87,120 ÷ 250 = about 348.5 feet deep. A 3-acre lot with 330 feet of road frontage runs 396 feet back. And a square acre is about 208.7 feet on each side.

Units and Conversions

Deeds, old plats and foreign-born listings use units you won't see on a tape measure. These are the conversions you'll meet:

Triangles

For a triangular lot, multiply the base by the height and divide by 2. The height is measured at a right angle to the base, and the slanted side doesn't count.

If all you have are the three side lengths, use Heron's formula. Add the sides and halve the total to get s. Then the area is the square root of s × (s − side one) × (s − side two) × (s − side three).

Trapezoids

Many lots are wider at one end than the other, with two sides running parallel. Add the two parallel sides, multiply by the distance between them, and divide by 2.

Irregular Parcels

Real parcels have angled sides, notches and curves. The usual trick is to cut the shape into rectangles, triangles and trapezoids, calculate each, add them up and divide by 43,560.

Four sides that aren't square

Four side lengths aren't enough to pin down a four-sided lot, because the same four sides can lean into many different shapes. You also need one diagonal. The diagonal cuts the lot into two triangles, and each triangle can be done with Heron's formula.

Many corners: the shoelace method

For a lot with five or more corners, there's a trick that works for any straight-sided shape. It's called the shoelace formula, because the crisscross multiplication looks like a laced shoe. Pick one corner as your starting point and write every corner as "feet east" and "feet north" from it. Then, going around the lot in order, multiply each corner's east distance by the next corner's north distance, multiply its north distance by the next corner's east distance, and subtract the second result from the first. Add up all those results and halve the total.

If you walk the corners the other way around, the sum comes out negative. Drop the minus sign. One warning: the east and north numbers must be distances in feet, and not raw latitude and longitude. A degree of longitude is shorter than a degree of latitude everywhere in the United States, so plugging in degrees gives a wrong answer.

Curved edges

For a curve, such as a creek bank, place corners every so often along it and treat the stretch as straight segments. More points give a closer fit. A full circle has an area of π × radius squared, so a circular acre has a radius of about 117.8 feet.

Metes-and-bounds descriptions in a deed give bearings and distances instead of corners. Working out an area from them takes surveyor-style math, and a mistake is easy to make. How to Read a Legal Description explains how those descriptions are built.

Why Your Number May Not Match the Recorded Acreage

• Rounding. Records often round to a tenth of an acre or less.
• "More or less." Many deeds say so. The stated area is a description, not a measured fact.
• Your measurement is approximate. A map outline or a walked path isn't a survey, and the parcel line itself has some error (see How Accurate Are Online Property Lines?).
• What's included. Some figures include or exclude road right-of-way or easements. One county assessor explains that it assesses only usable acreage, which can differ from the deed.
• Slope. Land area is the flat, horizontal area, as on a map, and not the surface of a hill.

If the difference is small, don't worry. If it's large, the record may contain a mistake, you may be looking at a different parcel, or the boundary may have changed, and a survey is how to settle it. See How to Measure Property Area and Perimeter for the methods.

A Note on the Survey Foot

Older deeds and surveys sometimes use the U.S. survey foot, which is 2 parts per million longer than the international foot (0.3048 meter exactly). NIST says the survey foot was deprecated at the end of 2022 and shouldn't be used after that except for historic and legacy work. For a lot you're calculating by hand, the difference between the two acres is far too small to show up (see How Big Is an Acre?).

Quick Mental Estimates

• 0.25 acre is about 10,890 square feet, such as a lot of roughly 90 × 120 feet.
• 0.5 acre is about 21,780 square feet.
• 10 acres is 435,600 square feet. A square 10-acre block is 660 feet on each side.
• 200 ft × 200 ft is 40,000 square feet, which is only about 0.92 acre.

Frequently Asked Questions

How many square feet are in an acre?

43,560. To convert square feet to acres, divide by 43,560. To convert acres to square feet, multiply.

How do I find acreage on a map?

Open a map that has a measurement tool, click each corner of the area in order, close the shape and read the result in acres. It's an estimate, since the answer depends on where you place the points.

How do I calculate acres from a legal description?

If the description names a lot in a recorded plat, the plat usually shows the lot's dimensions, and you can multiply them out. For metes-and-bounds descriptions, a surveyor or a deed-plotting program can compute it, and the deed's own acreage is often marked "more or less."

How many acres is 200 feet by 200 feet?

40,000 ÷ 43,560 = 0.92 acre.

Common Mistakes

• Dividing by 43,560 before converting yards or meters to feet.
• Using the slanted side of a triangle instead of its height.
• Running the shoelace method on latitude and longitude instead of feet.
• Treating a calculated number as more exact than the measurements behind it.
• Mixing up acres and square feet in a listing.

To see how a parcel's outline relates to its acreage, read How to Read a Parcel Map.

Sources

• U.S. Survey Foot: Revised Unit Conversion Factors (NIST) Acre, chain, rod, link and square mile definitions; international vs. survey foot.
• Ending the Era of the U.S. Survey Foot (NIST) Survey foot deprecated after December 31, 2022.
• About Assessor Parcel Maps (Sacramento County Assessor) Why assessed acreage can differ from the deed.
• What is the unit called an acre? (sizes.com) Acreage is horizontal area; square-acre side length.