Right triangle calculator
Calculator
The calculator needs JavaScript. The tables below give the same numbers for common cases.
How it is worked out
- Use the Pythagorean theorem a² + b² = c² and the sine rule sin A = a ÷ c.
- Result: a = 3, b = 4, c = 5.
| Inputs | Answer |
|---|---|
| You know: Both legs (a and b); Leg a: 3; Leg b: 4; Hypotenuse c: 5; Angle A: 36.87 | Legs 3 and 4, hypotenuse 5, angles 36.869898° and 53.130102°. |
| You know: Leg a and the hypotenuse c; Leg a: 5; Leg b: 12; Hypotenuse c: 13; Angle A: 36.87 | Legs 5 and 12, hypotenuse 13, angles 22.619865° and 67.380135°. |
| You know: Leg a and the angle A opposite it (degrees); Leg a: 10; Leg b: 4; Hypotenuse c: 5; Angle A: 30 | Legs 10 and 17.320508, hypotenuse 20, angles 30° and 60°. |
How to use it
A right triangle has one 90° angle. Knowing two legs, or a leg and the hypotenuse, or a leg and an acute angle is enough to find everything else with the Pythagorean theorem and the basic trigonometric ratios.
The calculator returns both legs, the hypotenuse, both acute angles, the area, the perimeter and the altitude to the hypotenuse.
Frequently asked questions
How do I solve a right triangle?
Use a² + b² = c² for sides and sin, cos or tan for angles.
Which angle is opposite leg a?
Angle A; sin A = a ÷ c.
What do the acute angles add up to?
90°.
Method: standard arithmetic shown step by step; no outside data is used. Checked 2026-11-12.
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General information only. Results are plain arithmetic on the numbers you enter; check anything important (money, health, school work) against your own records or the official source.