Pythagorean Theorem Calculator

In a right-angled triangle the square of the hypotenuse equals the sum of the squares of the other two sides: a² + b² = c². With legs of 3 and 4, c = √(9 + 16) = √25 = 5. With legs 5 and 12, c = 13. To find a missing leg, rearrange the formula: if the hypotenuse is 13 and one leg is 5, the other leg is √(169 − 25) = √144 = 12. Builders use the 3-4-5 rule to check that a corner is square, and surveyors, carpenters and pilots use it to find straight-line distances. The hypotenuse is always the longest side and sits opposite the right angle, so check which side you are solving for.