Pythagorean Theorem Calculator

In any right triangle the squares of the legs sum to the square of the hypotenuse — 3-4-5 being the famous integer case. It's the basis of distance itself: the straight-line distance between two points is just the theorem applied to their coordinate differences.

Carpenters check corners for square by marking 3 units along one edge, 4 along the other — the diagonal must measure exactly 5. Any multiple works (6-8-10), and the check needs nothing but a tape measure.