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Pythagorean Theorem Calculator

Free Pythagorean theorem calculator — find the hypotenuse or a missing side of a right triangle with a² + b² = c², plus the angles, area and perimeter, with the working shown.

abc

Hypotenuse

5

c = √(a² + b²) = √(3² + 4²) = √25 = 5

Angle opposite a
36.8699°
Angle opposite b
53.1301°
Area
6
Perimeter
12

What is the Pythagorean Theorem Calculator?

In a right-angled triangle, the square of the longest side (the hypotenuse) equals the sum of the squares of the other two: a² + b² = c². Knowing any two sides gives the third.

How to use it

  1. 1

    Choose what to find

    c, a or b.

  2. 2

    Enter the two known sides

    Any unit.

  3. 3

    Read the answer

    With the steps.

Features

  • Any missing side

    Hypotenuse or either leg.

  • Angles, area, perimeter

    Worked out too.

  • Diagram

    A scaled drawing of your triangle.

  • Working shown

    Each step of the formula.

Popular uses

  • Construction

    Check a corner is square (3-4-5 rule).

  • Ladders and ramps

    Length needed to reach a height.

  • Homework

    Trigonometry basics.

Frequently asked questions

What is the 3-4-5 rule?

A triangle with sides 3, 4 and 5 always has a right angle — builders use it to check corners.

Does it work for any triangle?

Only right-angled triangles.

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