Pythagorean Theorem Calculator
Find a triangle's hypotenuse or a missing leg using the Pythagorean theorem.
Assumptions used in this calculation
- Right triangle only: The formula a² + b² = c² is only valid for right triangles; inputs are assumed to describe a right triangle's sides.
About this calculator
Finding a right triangle's missing side comes up constantly in construction, navigation and geometry homework, and while the Pythagorean theorem itself is simple, rearranging a² + b² = c² to solve for a leg instead of the hypotenuse, and remembering to take the square root at the end, are common places to slip up. This calculator solves a² + b² = c² in both directions: given two legs, it finds the hypotenuse as c = √(a² + b²); given the hypotenuse and one leg, it rearranges to a = √(c² − b²) to solve for the missing leg instead. It's built specifically for right triangles (one 90° angle), since the theorem doesn't apply to any other triangle shape, for those the law of cosines used in the Triangle Calculator is the general-purpose tool. That handles the algebraic rearrangement automatically, so you just plug in whichever two sides you know.
Worked example
Legs 3 and 4
Result: Hypotenuse = 5
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