Triangle Calculator from Three Sides (Heron)
Triangle calculator from three sides: area with Heron’s formula, perimeter and all three angles.
A = √(s(s − a)(s − b)(s − c))
How to use this calculator
- Type your input in the box.
- The result updates as you type.
- Use “Copy result” or “Copy link” to share it.
With semi-perimeter s = (a + b + c)/2, the area is A = √(s(s − a)(s − b)(s − c)).
The angles follow from the law of cosines. The sides must satisfy the triangle inequality.
Frequently asked questions
Area of a 3-4-5 triangle?
6 (it is a right triangle).