Pythagorean Theorem Calculator

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Solve any side of a right triangle from the other two using the Pythagorean theorem, plus its area, perimeter and the two non-right angles. Free and instant.

b a c

Enter any two sides and leave the unknown one blank to solve it.

Leave exactly one field blank. Sides a and b are the legs; side c is the hypotenuse, the longest side opposite the right angle.
Solved side –
Area –
Perimeter –
Angle at a (opposite a) –
Angle at b (opposite b) –
Based on a² + b² = c². Area = ½ × a × b; angles are found with the arctangent of the legs.

About Pythagorean Theorem Calculator

The Pythagorean theorem calculator solves the missing side of a right triangle from the other two using a² + b² = c². Enter any two of the legs a and b or the hypotenuse c, leave the unknown one blank, and the tool finds it immediately.

Beyond the missing side, it computes the triangle’s area as ½ × a × b, its perimeter, and both non-right angles, found with the arctangent of the legs. That makes it a complete right-triangle solver rather than just a hypotenuse calculator.

It is handy for geometry homework, checking that a frame or wall is square, ladder placement and any diagonal-distance problem. Free, instant and entirely in-browser.

How to use Pythagorean Theorem Calculator

  1. Enter two of the three sides: leg a, leg b or hypotenuse c.
  2. Leave exactly one field blank — that is the side the calculator solves.
  3. Read the solved side in the result panel.
  4. Check the area, perimeter and the two non-right angles below it.

Frequently asked questions

Side c, the longest side, opposite the right angle. Sides a and b are the legs that form the right angle. If you know both legs, the calculator finds c as √(a² + b²).

Yes. Enter the hypotenuse and one leg, leave the other leg blank, and the tool solves it as √(c² − a²). The hypotenuse must be longer than the known leg.

From the arctangent of the legs. The angle opposite side a is arctan(a/b) and the angle opposite side b is arctan(b/a); together with the 90° angle they sum to 180°.

No — only right triangles. If your triangle has no 90° angle, a² + b² ≠ c², and you would need the law of cosines instead.

Any unit, as long as both known sides use the same one. The solved side and perimeter come out in that unit, and the area in its squared form.
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