Irregular Lot Area Calculator

Enter the four boundary sides and one corner-to-corner diagonal. The diagonal removes the guesswork that makes a four-side-only estimate unreliable.

Calculate your estimate

Side AB (ft)

Side BC (ft)

Side CD (ft)

Side DA (ft)

Diagonal AC (ft)Measure one corner-to-opposite-corner diagonal.

Enter the measurements above.

How to calculate an irregular four-sided lot

Answer first: four side lengths alone do not uniquely determine the area of a general quadrilateral. This calculator also asks for one diagonal so the lot can be split into two triangles. Each triangle is solved with Heron’s formula, then the two areas are added.

Formula

For each triangle, semi-perimeter s = (a + b + c) ÷ 2. Area = √[s(s−a)(s−b)(s−c)]. The total lot area is the sum of both triangle areas.

Accuracy: this method assumes straight boundary segments and accurate measurements. If the lot has more corners or curved boundaries, use the map tool or a survey drawing instead.

Frequently asked questions

Can I calculate a four-sided lot with only four side lengths?

Not uniquely in the general case. Different quadrilaterals can have the same four side lengths but different areas. One diagonal or angle is needed to fix the shape.

How many square feet are in one acre?

One acre equals 43,560 square feet.

Is this accurate enough for a legal property area?

No. It is a planning estimate. Legal boundary area should come from a recorded survey, deed or licensed surveyor.