Triangle Calculator
Choose what you know about the triangle, enter the values, and get every side, angle, the area and the perimeter.
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How the triangle is solved
- SSS (three sides): the law of cosines gives each angle: cos A = (b² + c² − a²) ÷ 2bc.
- SAS (two sides and the angle between them): the law of cosines gives the third side, then the remaining angles follow.
- ASA (two angles and the side between them): the third angle is 180° minus the other two, and the law of sines gives the other sides.
The area uses Heron's formula, √(s(s−a)(s−b)(s−c)) with s half the perimeter, which works for any triangle. The tool also names the triangle: equilateral, isosceles or scalene, and acute, right or obtuse.
Checks
Three sides only make a triangle if each is shorter than the other two together (the triangle inequality), and the angles of any triangle add up to 180°. For right triangles, the Pythagorean Theorem Calculator is quicker.
Free to useNo software to install — works in any modern browser.
No signup neededOpen the tool and start straight away.
Runs in your browserNothing you enter is sent to a server.
Works on mobileSame tool on your phone, tablet or desktop.
How it works
- Enter — type or paste your values or text.
- Get the result — it is worked out in your browser.
- Adjust — change the inputs to compare, or copy the result.
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