Triangle Calculator
Heron area from three sides, plus a Pythagoras solver.
Frequently Asked Questions
What is Heron formula?
It finds area from the three sides alone: with semi-perimeter s = (a + b + c) / 2, the area is √(s(s - a)(s - b)(s - c)). It works for any triangle, no angles or heights needed.
What is Pythagoras theorem?
In a right-angled triangle, the square of the hypotenuse equals the sum of the squares of the other two sides: c² = a² + b². The 3-4-5 triangle is the classic whole-number example.
Why did my three sides get rejected?
They violate the triangle inequality: any two sides together must be longer than the third side, otherwise the ends cannot meet to close the triangle.
Is the Triangle Calculator free, and is my data private?
Yes. It is completely free and every calculation runs locally in your browser, so the numbers and dates you enter are never uploaded, stored, or shared with anyone.
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