What is the Pythagorean Theorem Calculator?
The Pythagorean theorem calculator finds the longest side of a right triangle from the two shorter sides, or a missing leg when you know the hypotenuse.
How to use the Pythagorean Theorem tool
- Enter Find, Side A (leg), Side B (leg and or hypotenuse when finding a leg).
- The result updates instantly as you type, or press Calculate.
- Use Try an example to see how it works, and Reset to start again.
Formula
a² + b² = c², where c is the hypotenuse. To find a leg: a = √(c² − b²).
Worked example
With find Hypotenuse (enter both legs), side a (leg) 3, side b (leg, or hypotenuse when finding a leg) 4, the hypotenuse c comes to 5. Area: 6.
Frequently asked questions
Does it work for any triangle?
No. It applies only to right triangles that have a 90 degree angle.
What are Pythagorean triples?
Whole-number sets that satisfy the theorem, such as 3-4-5 and 5-12-13.
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Checked by Calcovate · Formula tested against worked examples · Updated 7 Nov 2026 · How we check our calculators.