Triangle Calculator
Calculate area (Heron's formula), perimeter, and angles from three side lengths.
Formula
s = (a+b+c)/2, A = √(s(s-a)(s-b)(s-c))
Heron's formula: compute the semi-perimeter s, then area = √(s(s-a)(s-b)(s-c)).
Examples
3-4-5 right triangle
5-12-13 right triangle
Equilateral (5-5-5)
Frequently Asked Questions
What is Heron's formula?
Heron's formula calculates triangle area from three sides: A = √(s(s-a)(s-b)(s-c)) where s = (a+b+c)/2.
How do I find the angles of a triangle from its sides?
Use the Law of Cosines: cos(A) = (b²+c²-a²)/(2bc).
What is the perimeter of a triangle?
The perimeter is simply a + b + c.
About this Calculator
Calculate area (Heron's formula), perimeter, and angles from three side lengths. All calculations are performed in your browser for instant results. Formulas are mathematically exact using JavaScript's built-in Math functions.