Pythagorean Theorem Calculator

Enter two sides of a right triangle to find the third, using a² + b² = c².

How to Use the Pythagorean Theorem Calculator

It doesn't matter which two sides get filled in first — leg-and-leg or leg-and-hypotenuse both work, and the calculator infers which case applies from what's missing.

a² + b² = c²

Two legs and a hypotenuse, and knowing any two gets you the third: c = √(a² + b²), or rearranged, a = √(c² − b²) and b = √(c² − a²). This Pythagorean Theorem Calculator solves for whichever side you're missing. The hypotenuse — always "c" here — is the longest side, sitting opposite the right angle; it's never one of the two legs that form that angle.

The theorem is geometric before it's algebraic: build an actual square on each of the triangle's three sides, and the two smaller squares' combined area exactly equals the big one's. That's the original insight the formula compresses into three letters.