About the Pythagorean theorem
This calculator solves a right-angled triangle using the Pythagorean theorem, a² + b² = c². Enter any two sides and it finds the third — whether you are missing a leg or the hypotenuse. It runs in your browser.
How Pythagorean works
How to use it
- Enter any two of the three sides.
- Leave the side you want blank.
- Read the missing side.
How it works
For a right triangle, the square of the hypotenuse (c, the longest side) equals the sum of the squares of the other two sides. So c = √(a² + b²), and a leg = √(c² − other²).
Common uses
- Find a missing triangle side
- Calculate a hypotenuse
- Check a right angle
- Help with geometry homework
- Work out a diagonal length
- Lay out a square corner
- Solve construction measurements
- Learn the Pythagorean theorem
Frequently asked questions
What is the Pythagorean theorem?
a² + b² = c² for a right-angled triangle, where c is the hypotenuse.
Which side is c?
The hypotenuse — the longest side, opposite the right angle.
How many sides do I enter?
Any two; the tool finds the third.
Is my input uploaded?
No — it calculates in your browser.
Can it find a leg?
Yes — leave a or b blank and enter c and the other leg.
Does it only work for right triangles?
Yes — the theorem applies to right-angled triangles.
Is it free?
Yes — completely free with no sign-up.