How it works
a² + b² = c²
- a, b — the two shorter sides (legs)
- c — the hypotenuse, opposite the right angle
To find a leg, rearrange: b = √(c² − a²). Builders use the 3-4-5 triangle to check corners are square: 3² + 4² = 5².
Pythagorean theorem calculator
Choose what you want to find. Enter the two sides you know to get the third side of the right triangle, with its area, perimeter and angles.
Missing side
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Common questions
Does it work for any triangle?
Only right triangles, which have one 90° angle.
What are Pythagorean triples?
Whole-number sides that fit the theorem, such as 3-4-5, 5-12-13 and 8-15-17.