Pythagorean Theorem Calculator
Pick the unknown side. Click any i for detail.
Triangle
Solve for
i
Unknown
Hypotenuse c, or a leg. |
|
|---|---|
a (leg)
i
a
One leg. Hidden when a is the unknown. |
|
b (leg)
i
b
The other leg. Hidden when b is the unknown. |
|
c (hypotenuse)
i
c
Longest side. Hidden when c is the unknown. |
How to use this calculator
- Choose which side is unknown.
- Enter the other two.
- Read the third side.
- Quadratic formula is a different algebra page.
Results explained
c = √(a² + b²). A leg is √(c² − other²) when c is longer.
Quick reference: 3-4-5
The classic integer triple: 3² + 4² = 5².
| Item | Detail |
|---|---|
| 3-4-5 | Right triangle |
| 5-12-13 | Another triple |
| Square footage | Rectangles, not hypotenuses |
| Quadratic | ax² + bx + c = 0 |
Obtuse or acute non-right triangles need law of cosines — not here.
How the estimate is built
a² + b² = c².
Example scenario
a = 3, b = 4 → c = 5.
FAQ
Units?
Any, as long as all three match.
3D diagonal?
That’s √(x²+y²+z²) — not this 2-D page.
Stairs?
See the stair calculator for risers/treads.