Triangle Calculator

Area is calculated using Heron's formula, which finds a triangle's area purely from its three side lengths without needing a height measurement: first the semi-perimeter (half the perimeter) is found, then the area is the square root of semi-perimeter times each side subtracted from it in turn.

The three angles are found using the law of cosines, which relates each angle to the lengths of all three sides. This calculator checks the triangle inequality first (each side must be shorter than the sum of the other two) to make sure the three lengths you enter can actually form a triangle.