Pythagorean Theorem Calculator
Find the missing side of a right triangle with a² + b² = c² — the hypotenuse from two legs, or a leg from the hypotenuse and the other leg.
How to use
- 1Choose which side is missing.
- 2Enter the two sides you know.
How it's calculated
c = √(a² + b²) for the hypotenuse; a = √(c² − b²) for a leg.
Frequently asked questions
Which side is the hypotenuse?
The longest side, opposite the right angle.
What are Pythagorean triples?
Whole-number sides that fit exactly, like 3-4-5, 5-12-13 and 8-15-17.
How do builders use this?
The 3-4-5 rule checks a corner is square: measure 3 ft along one side and 4 ft along the other; the diagonal should be exactly 5 ft.