Pythagorean Theorem Calculator

In a right triangle, the square on the hypotenuse equals the sum of the squares on the other two sides. The rule appears in India’s Baudhayana Sulba Sutra as well as in Pythagoras.

Find
Results update as you type.

Hypotenuse c

5

Area
6
Perimeter
12

About this calculator

Choose whether you need the hypotenuse or a leg.

How to use it

  1. Choose what to find.
  2. Enter the two known sides.
  3. Read the missing side.

The formula

c² = a² + b²
c
hypotenuse, opposite the right angle

Worked example

Legs 3 and 4

  1. c = √(9 + 16) = 5.
  2. Area = 6; perimeter = 12.

What the result means

3-4-5, 5-12-13 and 8-15-17 are whole-number (Pythagorean) triples.

Assumptions

  • All lengths in the same unit.

Limitations

  • Results are rounded to 10 significant figures.

Frequently asked questions

How do I find the hypotenuse?

√(a² + b²).

How do I find a leg?

√(c² − a²).

Does it work for any triangle?

Only right triangles; use the law of cosines otherwise.

Last reviewed on 3 October 2026. Found a mistake? Tell us.