The Pythagorean theorem (a² + b² = c²) is one of the most fundamental relationships in geometry, describing how the sides of a right triangle relate to each other. This Pythagorean theorem calculator finds any missing side of a right triangle when you know the other two, whether that's calculating the hypotenuse from the two legs, or finding a leg when you know the hypotenuse and the other leg. It's widely used in construction, navigation, physics, and everyday problem-solving involving right angles, such as finding the diagonal of a rectangle or the length of a ladder needed to reach a certain height. Simply leave the unknown field blank and the calculator solves for it instantly.