Pythagorean Theorem

This calculator finds a missing side of a right triangle for students, builders, and anyone checking a diagonal measurement.

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Enter the lengths of any two sides. Use a and b for the legs that meet at the right angle, and c for the hypotenuse, which is the longest side.

The calculator uses a² + b² = c². To find a leg, rearrange it as a = square root of (c² - b²) or b = square root of (c² - a²).

Worked example

A rectangular frame is 3 feet high and 4 feet wide. Its diagonal is c = square root of (3² + 4²) = 5 feet.

No. The Pythagorean theorem applies only to triangles with one 90-degree angle.

It is the side opposite the right angle. It is also the triangle's longest side.