# Right triangle calculator

> A right triangle has one 90° angle. Enter any two known values — any two sides, or one side and one angle — and the calculator fills in the rest.

Solve a right triangle from any two known values — sides or angles. Returns all sides, both acute angles, area, and perimeter.

**Interactive version:** https://onlinecalculator.me/math/right-triangle/
**Category:** Math

## Formula

```
Pythagorean theorem: a² + b² = c²

Angles:
  angle A = arctan(a / b)
  angle B = arctan(b / a) = 90° - angle A

Area = ½ × a × b
Perimeter = a + b + c
```

## Common Pythagorean triples

| a | b | c |
|---|---|---|
| 3 | 4 | 5 |
| 5 | 12 | 13 |
| 8 | 15 | 17 |
| 7 | 24 | 25 |

## Frequently asked questions

### What is a right triangle?

A right triangle is a triangle with one 90° angle. The side opposite the right angle is the hypotenuse (c), the longest side. The other two sides are called legs (a and b).

### What is the Pythagorean theorem?

For a right triangle: a² + b² = c². Given any two sides, the third can be found by rearranging this equation.

### How do you find a missing angle?

If you know both legs: angle A = arctan(a/b). If you know one leg and the hypotenuse: angle A = arcsin(a/c). The two acute angles always sum to 90°.

### What is a 3-4-5 triangle?

A 3-4-5 triangle is a Pythagorean triple: legs 3 and 4, hypotenuse 5. Other common triples include 5-12-13, 8-15-17, and 7-24-25.

### How do I share my calculation?

Click "Share with my numbers" to copy a URL that saves your two known values.

## Sources

- [Right triangle](https://en.wikipedia.org/wiki/Right_triangle) — Wikipedia
- [Pythagorean theorem (a² + b² = c²)](https://en.wikipedia.org/wiki/Pythagorean_theorem) — Wikipedia

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