Irregular Lot Acreage Calculator
Two ways to measure an odd-shaped lot: trace the boundary on a satellite map, or use tape measurements of the sides and a diagonal.
Four sides + diagonal
- Square feet
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- Square meters
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- Hectares
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- Square yards
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Or trace the lot on a map
Search an address, then click around the edge of the land to outline it. Drag the white points to adjust. The area updates as you draw.
- Square feet
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- Square meters
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- Hectares
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- Perimeter
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- Points
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Map accuracy depends on imagery alignment and how carefully the boundary is traced; expect a few percent of error. For legal boundaries, use a licensed survey or your county parcel records.
How the four-sides method works
Label the sides A, B, C and D going around the lot. Measure the diagonal that runs from the corner where A meets B to the opposite corner where C meets D. That diagonal cuts the lot into two triangles: one with sides A, B and the diagonal, the other with sides C, D and the diagonal. Each triangle’s area comes from Heron’s formula:
s = (a + b + c) ÷ 2 · area = √(s(s−a)(s−b)(s−c))
Add the two triangle areas and divide by 43,560 to get acres. Measuring the diagonal is what makes the result exact; averaging opposite sides (a common shortcut) can be off by 10% or more on skewed lots.
Frequently asked questions
Can I calculate the area of an irregular lot from four sides only?
No. Four side lengths do not fix the shape; the same sides can enclose very different areas. You also need one diagonal (or the angles). With the diagonal, the lot splits into two triangles that can be solved exactly.
What if my lot has more than four sides?
Trace it on the map, or split it into triangles yourself, measuring every side and enough diagonals, and add the triangle areas.
Where can I find exact lot dimensions?
Your deed, plat map or survey lists bearings and distances. Many county GIS or appraisal district websites also show parcel boundaries and areas.