In a right triangle, the square of the hypotenuse (the side opposite the right angle) equals the sum of the squares of the other two sides. Enter any two sides to find the third, along with the triangle’s area and perimeter.
Formula
c^2 = a^2 + b^2
Where a is the side a (leg), b is the side b (leg), c is the side c (hypotenuse).
Choose any value to calculate — the calculator rearranges the formula for you.
Worked example
A right triangle with legs of 3 and 4 has a hypotenuse of √(3² + 4²) = √25 = 5. This 3-4-5 triangle is the best-known Pythagorean triple.
Frequently asked questions
How do I find the hypotenuse?
c = √(a² + b²). Square both legs, add them, and take the square root.
How do I find a missing leg?
a = √(c² − b²). Choose the leg under Calculate and enter the other leg and the hypotenuse.
Last updated · Calculations checked by automated tests· Editorial policy