🔺 Pythagorean Theorem Calculator
In any right triangle, the square of the hypotenuse equals the sum of the squares of the two legs: a² + b² = c². It is the most used theorem in geometry — behind maps, construction layouts and game physics.
Choose what to solve for. To find the hypotenuse, enter both legs; to find a missing leg, enter the hypotenuse as Side A and the known leg as Side B.
How to use this calculator
Choose whether to find the hypotenuse or a missing leg, enter the two known sides, and press Calculate.
- Pick Solve for: Hypotenuse if you know both legs, or Missing leg if you know the hypotenuse and one leg.
- Type the first known side into Side A; in leg mode this must be the hypotenuse.
- Type the second known side into Side B; in leg mode this is the known leg.
- Press Calculate and read the missing side as the headline result.
Frequently asked questions
What is the Pythagorean theorem?
In a right triangle, the square of the hypotenuse equals the sum of the squares of the two legs: a squared + b squared = c squared. It only applies to triangles with a 90-degree angle.
How do I find the hypotenuse?
Square both legs, add them, and take the square root. Legs of 3 and 4 give 9 + 16 = 25, whose square root is 5.
How do I find a missing leg?
Square the hypotenuse, subtract the square of the known leg, and take the square root. A hypotenuse of 5 and a leg of 3 give 25 - 9 = 16, whose square root is 4.
Why did I get a hypotenuse-must-be-longer error?
In missing-leg mode the hypotenuse (Side A) must be longer than the known leg (Side B); otherwise no real triangle exists. Swap the values if you entered them backwards.