How to use Triangle Calculator
- Enter the lengths of sides a, b and c.
- Check the triangle is valid.
- Read the area, perimeter, angles and triangle type.
About this tool
Area is found with Heron's formula, which needs only the three sides, and the angles come from the law of cosines. A triangle is valid only if each side is shorter than the sum of the other two.
The type is reported both by sides (equilateral, isosceles, scalene) and by angles (acute, right, obtuse).
Frequently Asked Questions
- What if my triangle is not valid?
- If one side is as long as or longer than the other two combined, the sides cannot meet and the calculator reports an error.
- Do angles add up to 180 degrees?
- Yes, the three angles of a flat triangle always sum to 180 degrees.
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