Find a missing side of a right triangle, or check if three sides form one — free and instant.
The Pythagorean theorem relates the three sides of a right triangle: a² + b² = c², where c is the hypotenuse (the longest side, opposite the right angle). Enter any two sides and leave the third blank to solve for it, or switch modes to check whether three given side lengths actually form a right triangle at all.
For the missing-side mode: entering the hypotenuse (c) as blank alongside sides a and b finds the hypotenuse; entering a or b as blank alongside the other two finds that leg.
Worked example: a right triangle has legs of 6 and 8. To find the hypotenuse: c² = 6² + 8² = 36 + 64 = 100, so c = √100 = 10. A common mistake is applying the formula the same way regardless of which side is missing — if you're solving for a leg instead of the hypotenuse, you need to rearrange it to a² = c² − b² (subtract, not add), since the hypotenuse is always the longest side.
It sorts your three numbers, treats the largest as the hypotenuse, and checks whether the sum of the squares of the other two exactly equals its square.
The theorem itself only applies to right triangles — use the Triangle Solver instead for a general triangle without a right angle.
Yes — both modes work with decimals, not just whole numbers.