📏 Pythagorean Theorem Calculator

About this Pythagorean Theorem Calculator

This Pythagorean calculator finds the unknown side of a right-angled triangle from the two known sides, using a² + b² = c². It works both ways: square and add the legs to get the hypotenuse, or subtract to recover a missing leg — useful for building, layout work, screen sizes and maths homework.

How to use it

1. Choose which side you want to find: the hypotenuse or one of the legs.
2. Enter the two side lengths you already know.
3. Click Find the missing side.

Example

A triangle with legs 3 and 4 has a hypotenuse of exactly 5 — the famous 3-4-5 triangle used by builders to check square corners.

Frequently asked questions

Which side is the hypotenuse?

The longest side, always opposite the right angle. It is labelled c in the formula a² + b² = c².

Does it work for any triangle?

No — the theorem only holds for right-angled triangles, the ones with one exact 90° corner.

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