Triangle Area Calculator

About this calculator

A triangle's area is half its base times its height: A = ½ × b × h. The height must be measured perpendicular to the base — the straight-line distance from the base to the opposite corner, not the length of a slanted side.

Any side can serve as the base; pick whichever one you know the perpendicular height for. The ½ appears because every triangle is exactly half of the parallelogram you'd get by duplicating and rotating it.

Only have the three side lengths? Heron's formula covers that case: with s as half the perimeter, A = √(s(s−a)(s−b)(s−c)).