Right Triangle Calculator
Any two sides give the third, the area and both angles.
Work out Right Triangle. Any two sides give the third, the area and both angles. Free, with no account and nothing to download.
Fill in any two of the three. Leave the one you want blank or at zero.
Hypotenuse
5
legs 3 and 4 · area 6
a² + b² = c², with c always the hypotenuse — the side opposite the right angle, and always the longest. The two non-right angles sum to 90°, since the three must total 180°. Whole-number triples like 3-4-5, 5-12-13 and 8-15-17 are called Pythagorean triples and are worth recognising: they turn up constantly in exam questions precisely because they avoid awkward square roots.
How the Right Triangle Calculator works
Enter any two of the three sides and leave the third blank. You get the missing side, the area, the perimeter and both non-right angles. A leg longer than the hypotenuse is refused rather than producing an imaginary result.
Also known as: hypotenuse calculator · find the missing side of a right triangle · right angle triangle calculator · pythagorean triple calculator
Frequently asked questions
How do I find the missing side of a right triangle?
a² + b² = c². For the hypotenuse, add the squares of the legs and take the root. For a leg, subtract its square from the hypotenuse's and take the root.
Which side is the hypotenuse?
The one opposite the right angle, and always the longest. If a value you have entered as a leg exceeds the hypotenuse, one of the two is mislabelled — that triangle cannot exist.
What are Pythagorean triples?
Whole-number side sets like 3-4-5, 5-12-13 and 8-15-17. They appear constantly in exam questions precisely because they avoid awkward square roots, so recognising a few saves time.
How do I find the angles?
From the inverse tangent of the opposite over the adjacent side. The two non-right angles always sum to 90°, since all three must total 180°.
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