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Pythagoras' Theorem Calculator
Pythagoras' theorem for a right-angled triangle — enter 2 sides.
Find a side
Diagram for illustration only — not to scale
Examples
How to use it
- Pythagoras' theorem: in any right-angled triangle, the square of the hypotenuse equals the sum of the squares of the two legs — c² = a² + b².
- Choose which side is unknown: a or b (a leg) or c (the hypotenuse — the side opposite the right angle).
- Enter the two known sides; they must be positive numbers.
- Note: when finding a leg, the hypotenuse must be the longest side.
- The result is rounded to 4 decimal places and shown with a guided solution.
Related tools
- Quadratic Equation Solver — square roots, the discriminant and completing the square.
- Perimeter & Area — work out the area of a right-angled triangle when you know the sides.
- Function Grapher — visualise geometric relationships on a graph.
✍️ Written by the MathsUK teamChecked against the National Curriculum and GCSE specifications