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About the Triangle Calculator
The Triangle Calculator computes the area, perimeter, angles, and side lengths of a triangle from the values you provide. It works with right, isosceles, and equilateral triangles. You receive every result at once after a single entry.
Enter any three valid values, such as three sides, two sides with the included angle, or a base and height. The calculator uses standard geometry, including Heron's formula A = √(s(s-a)(s-b)(s-c)) for the area of three known sides, the Pythagorean theorem for right triangles, and the law of cosines for missing angles. Keep all inputs in the same unit. Also confirm your side lengths obey the triangle inequality, so each side is shorter than the sum of the other two.
- Choose the triangle type and pick the values you know.
- Enter three measurements, such as three side lengths.
- Press calculate to see the area, perimeter, and angles.