Quick start
- Choose whether to find the hypotenuse, leg a, or leg b.
- Enter the two known side lengths.
- Add a unit label if useful.
- Press Calculate side to solve the missing side.
When the theorem applies
The Pythagorean theorem only works for right triangles. The hypotenuse is always the side opposite the 90-degree angle.
If the triangle is not a right triangle, use the Triangle Calculator instead.
Finding the hypotenuse
When both legs are known, the calculator uses c = sqrt(a^2 + b^2).
The hypotenuse should always be longer than either leg.
Finding a missing leg
When the hypotenuse and one leg are known, the calculator subtracts the known leg squared from the hypotenuse squared, then takes the square root.
If the known leg is longer than the hypotenuse, the input cannot describe a real right triangle.
Examples from the calculator
c = 5
a = 5
b = 15
History, privacy, and copying
Recent answers stay visible in the page while you work. The history is kept only in the current browser tab and is not sent to a server.
Copy answer copies the expression and result so you can paste it into notes, homework, a message, or another document.