Triangle Calculator
Use three sides to validate and analyze a triangle with Heron’s formula and the law of cosines.
How to use
- 1Enter three valid sides and review measurements and classification.
About
Validates the triangle inequality and identifies side and angle types.
Triangle calculator
Calculate area, perimeter, angles and triangle classification from its three sides.
Area uses Heron’s formula: A = √[s(s-a)(s-b)(s-c)], where s is the semiperimeter.
Enter sides a, b and c. Angles are calculated with the law of cosines.
Side classification is equilateral, isosceles or scalene; angle classification is acute, right or obtuse.
Practical examples
- Sides 3, 4 and 5 → area 6, perimeter 12 and a right triangle.
Limitations and notes
- Sides must be positive and each side must be shorter than the other two combined.
- Use valid values and keep all units consistent.
How to use
- 1Enter all three sides.
- 2Check the triangle inequality.
- 3Review area, angles and classifications.
Frequently asked questions
Can I enter angles instead?
This version derives angles from three sides. Angles alone need another side or scale to define the triangle.
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