Pythagorean Theorem Calculator
Solves a right triangle's missing side using the Pythagorean theorem from the other two sides.
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How to use this calculator
- Enter any two sides of a right-angled triangle.
- Press Calculate for the third side.
How it works
For a right-angled triangle, a² + b² = c², where c is the hypotenuse (the longest side). Enter any two sides and the calculator finds the missing one.
Worked example
Sides 3 and 4. c = √(3² + 4²) = √25 = 5.
Common mistakes
- Solving for a leg but using the hypotenuse formula — subtract, don't add, when finding a short side.
- Assuming any triangle works; the theorem applies only to right-angled triangles.
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 other two sides: a² + b² = c².
How do I find a missing leg?
Rearrange to a = √(c² − b²): subtract the known leg's square from the hypotenuse's square, then take the square root.
Does it only work for right triangles?
Yes — the theorem applies to right-angled triangles only.
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Cite this tool
Zerdly. (2026). Pythagorean Theorem Calculator. Retrieved from https://www.zerdly.com/tools/pythagorean-theorem-calculator/
Tip: Enter any known values to calculate the remaining results.
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