Area of a Triangle Calculator

This calculator finds the area of a triangle in the two ways the information usually arrives. The first and simplest is from the base and the perpendicular height, where the area is just half the base times the height. The second is Heron's formula, which you reach for when you know the three side lengths but not the height, a common situation in surveying, construction and land measurement where you can measure the edges of a triangular block but not its internal height. To use Heron's formula the calculator first finds the semi-perimeter, which is half the sum of the three sides, then takes the square root of the semi-perimeter multiplied by its difference from each side in turn. Before doing so it checks the triangle inequality, the rule that each side must be shorter than the sum of the other two, because three lengths that break this rule cannot close into a triangle and have no area. Triangular areas come up when working out a garden bed, a gable end, a section of roof, an offcut of material or a piece of land, so being able to switch between the base and height method and the three sides method is genuinely useful. Choose your method and enter the measurements to see the area instantly.

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