Right-triangle requirement
The Pythagorean theorem applies only when sides a and b meet at a 90-degree angle. For general triangles, use a triangle calculator.
Example
If side a is 3 and side b is 4, the hypotenuse is sqrt(3^2 + 4^2) = 5.
How to use the result
The hypotenuse is the side opposite the right angle. The same relationship is useful for diagonal measurements, construction checks and coordinate distance problems.
Common mistakes
Do not use this formula for a triangle that is not right-angled. Also make sure a and b are the two perpendicular sides, not the hypotenuse.
Limitations
The calculator assumes flat Euclidean geometry and positive side lengths.
Last reviewed: 2026-05-17