Triangle Calculator

Enter the three side lengths of a triangle to find its area and all three angles.

How this calculator works

The area is calculated using Heron's formula from the three side lengths, and each angle is found using the law of cosines.

Area = √( s(s−a)(s−b)(s−c) ), where s = (a+b+c)/2
If the three sides can't form a valid triangle, no result is shown.

Frequently asked questions

What if my three sides can't form a triangle?

Any side must be shorter than the sum of the other two — if that's not true, no valid triangle exists and the calculator won't return a result.

What is Heron's formula used for?

It calculates a triangle's area directly from its three side lengths, without needing to know any angles first.