Calcolatrice teorema di Pitagora
The detailed guide below is currently available in English.
What the theorem says
In any right triangle, the square of the hypotenuse equals the sum of the squares of the two legs: a² + b² = c². Knowing any two sides is therefore enough to recover the third. To find the hypotenuse, add the squares of the legs and take the square root; to find a leg, subtract the known leg's square from the hypotenuse's square first. The subtraction only works when c is genuinely the longest side, which is why entries with c shorter than a leg are rejected.
Recognizing right triangles
The theorem runs both directions: if three lengths satisfy a² + b² = c², the triangle they form has a right angle between a and b. That is the principle behind the 3-4-5 rope trick used to square up corners on construction sites — any multiple such as 6-8-10 works too. Whole-number examples like these are rare enough that they have their own name, Pythagorean triples.
Domande frequenti
Can I use this on a triangle without a right angle?
No. The plain theorem applies only when one angle is exactly 90°. For general triangles with three known sides, the triangle calculator uses the law of cosines instead.
Why was my leg rejected as "too long"?
A leg can never reach the hypotenuse, let alone exceed it — the hypotenuse faces the largest angle in the triangle. If your computed leg comes out longer than c, one of the entered values is probably mislabeled.