📐 Pythagorean Theorem Calculator
Know two sides of a right triangle? Find the third. Choose whether you are finding the hypotenuse or a leg.
Missing side
How the Pythagorean Theorem Calculator works
In a right triangle, the square of the hypotenuse equals the sum of the squares of the other two sides.
a² + b² = c²
c = √(a² + b²) · a = √(c² − b²)
Step-by-step calculation
- 1Choose what to find.
- 2Enter the two known sides.
- 3Apply a² + b² = c².
Worked example
Legs 3 and 4: c = √(9 + 16) = √25 = 5. Area = 3 × 4 ÷ 2 = 6.
Pythagorean Theorem Calculator examples
| Side a (or hypotenuse c) | Missing side |
|---|---|
| 2 | c = 4.472136 |
| 3 | c = 5 |
| 4 | c = 5.656854 |
| 5 | c = 6.403124 |
Other inputs kept at the calculator's default values. Results calculated by this calculator.
Why use a Pythagorean Theorem Calculator?
Find missing sides for construction, geometry and design.
Important factors that can affect your results
- Only right triangles.
- Same units for all sides.
- Hypotenuse must be the longest side.
Frequently asked questions
Which side is the hypotenuse?
The longest side, opposite the right angle.
Does it work for other triangles?
No — only right triangles. Use the law of cosines otherwise.
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Last reviewed November 2026 · How we build and check our tools · Report a problem