Pythagorean Theorem Calculator
Find the missing side of a right triangle, plus its angles, area and perimeter.
The theorem
a² + b² = c²
In any right triangle, the squares of the two legs add up to the square of the hypotenuse. Legs 3 and 4 give a hypotenuse of √25 = 5, the most famous of the Pythagorean triples (3-4-5, 5-12-13, 8-15-17, 7-24-25). Multiples of a triple are triples too, which is why builders check square corners with a 6-8-10 tape measurement.
Finding a leg instead
Rearrange: a = √(c² - b²). The hypotenuse is always the longest side, so if your 'leg' comes out longer than the hypotenuse, the two values are swapped.