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.
Enter any two known values (sides a, b, c or an acute angle).
Side a
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Side b
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Hypotenuse c
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Angle A
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Angle B
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Area
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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
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.