What is Heron's formula?

Area = √(s·(s−a)·(s−b)·(s−c)) where s = (a+b+c)/2 is the semi-perimeter. It works for any valid triangle from side lengths alone.

How are the angles computed?

Using the Law of Cosines: cos A = (b² + c² − a²)/(2bc), and similarly for B and C. The three angles always sum to 180°.

The tool shows a clear warning if the triangle inequality (a+b>c, a+c>b, b+c>a) is violated.

Yes — any positive numbers are supported. The output is rounded to four decimals for readability.

Yes — everything runs in your browser.

Area (Heron's), perimeter and angles from three sides.

100% private — no uploads Free & unlimited Read tutorial

Watch a quick simulation of this tool in action — no file needed.

Follow these steps — everything happens instantly in your browser.

1
Step 1. Enter the three side lengths (a, b, c).
2
Step 2. The calculator checks triangle validity (sum of any two sides must exceed the third).
3
Step 3. See area (Heron's), perimeter, semi-perimeter and all three angles instantly.

Everything you might want to know about triangle calculator.

Area, circumference, diameter — and 90° arc & sector — from radius.

a² + b² = c² — solve for any side of a right triangle.

Range, max height, time of flight — for any launch angle and velocity.

Solve ax² + bx + c = 0 — real and complex roots, with discriminant.