Pythagorean Theorem Calculator

Enter two legs to get the hypotenuse, or the hypotenuse and one leg to get the other leg. All three lengths share the unit you pick.

How it works

In a right triangle the legs a and b and the hypotenuse c satisfy a² + b² = c². Solving for c is √(a²+b²). Solving for a missing leg is √(c²−a²), which is only defined when c is strictly longer than that leg.

This page does not compute angles or area — the right-triangle calculator does.

Formula

a² + b² = c²
c = √(a² + b²)
b = √(c² − a²)

Worked examples

Find the hypotenuse
legs 3 and 4 → 5
Find a leg
hypotenuse 5, other leg 3 → 4

Useful notes

Only right triangles. An obtuse 3-4-6 is not a Pythagorean triple.

FAQ

What is the Pythagorean theorem?: In a right triangle, the square of the hypotenuse equals the sum of the squares of the legs: a² + b² = c².
Why was my missing-leg calculation rejected?: The hypotenuse must be longer than the known leg. If they are equal, the other leg would be 0, which is not a triangle.
Does this give the angles too?: No. Use the right-triangle calculator when you also want angles, area and perimeter.

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