Right Triangle Calculator
Enter any two of a right triangle's sides (two legs, or one leg and the hypotenuse) to calculate everything else.
Last updated: September 5, 2026
Frequently asked questions
What is the hypotenuse of a right triangle with legs 3 and 4?
5 - using the Pythagorean theorem: c = √(3² + 4²) = √25 = 5. This is the classic 3-4-5 right triangle.
How do I find a missing leg if I know the hypotenuse and one leg?
Rearrange the Pythagorean theorem: missing leg = √(hypotenuse² − known leg²). For example, with hypotenuse 5 and one leg 3: √(25−9) = √16 = 4.
How do I find the angles of a right triangle from its sides?
Once you know all three sides, use inverse sine: angle A = sin⁻¹(a ÷ c), where a is the leg opposite angle A and c is the hypotenuse. The other non-right angle is simply 90° minus angle A, since all three angles sum to 180°.
What's the area of a right triangle?
0.5 × leg a × leg b - the two legs meet at the right angle, so they serve directly as the triangle's base and height.
Can I solve a right triangle if I only know one side and one angle?
No - this calculator requires two known sides (any two of the two legs and the hypotenuse) to apply the Pythagorean theorem. If you only have one side and one angle, you'd need trigonometric ratios (sine, cosine, tangent) instead, which this tool doesn't take as direct inputs.
How do I check that three side lengths actually form a valid right triangle?
Verify that the square of the longest side equals the sum of squares of the other two (a² + b² = c²). For sides 6, 8, and 10: 6² + 8² = 36 + 64 = 100 = 10², confirming a valid right triangle.
What's the difference between this and a general (non-right) triangle calculator?
This tool relies on the Pythagorean theorem, which only holds when one angle is exactly 90° - a general triangle (acute or obtuse) needs the Law of Sines or Law of Cosines instead, since side-angle relationships aren't as simple without a right angle.