Irregular Plot Area Calculator
Works out the area of a plot that is not a rectangle.
Plot area
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Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
Acres — acres
Perimeter, for fencing —
Reading this —
The formula
triangle area = √(s(s − a)(s − b)(s − c)), s = half the perimeter
The diagonal splits the plot into two triangles, and Heron’s formula gets each area from its three sides.
What to watch out for
Sides A and B should form a triangle with the diagonal, with C and D forming the other on its far side.
Frequently Asked Questions
Why do I need a diagonal?
Four sides alone do not fix a shape: the same sides can lean into different areas. A diagonal locks it into two triangles.