Triangle Calculator
Calculate triangle properties: area, perimeter, angles, and type from three sides — all in your browser, instant results.
About the Triangle Calculator
This triangle calculator runs entirely in your browser. Enter the three sides of a triangle, and the tool computes the area, perimeter, all three angles, and the triangle type (equilateral, isosceles, scalene, right, obtuse, or acute).
How it works
- Validity: A triangle is valid when the sum of any two sides is greater than the third.
- Area: Computed via Heron's formula using the semi-perimeter
s = (a+b+c)/2:Area = √(s(s−a)(s−b)(s−c)). - Angles: Derived using the law of cosines:
cos A = (b² + c² − a²) / (2bc). - Type: Determined by side equality and the largest angle's relation to 90°.
Frequently asked questions
Does this tool upload my data? No. All calculations happen locally in your browser.
What if the sides don't form a valid triangle? The tool will report that the triangle is invalid and not compute the rest.
Are decimals and negative values supported? Decimals are supported. Negative or zero side lengths are rejected.
Why are angles in degrees? Degrees are the most common format. Each angle is rounded for display but computed precisely.