Triangle Calculator
Calculates a triangle's area and perimeter from its three sides.
Lilu Baba's Triangle Calculator uses Heron's formula to compute area from any three valid side lengths, along with the perimeter.
How to use this calculator
- Enter the lengths of all three sides.
- Area (via Heron's formula) and perimeter update instantly.
Area (Heron's Formula)
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Perimeter
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FAQ
Triangle Calculator — frequently asked questions
Area = √(s(s−a)(s−b)(s−c)), where s is the semi-perimeter ((a+b+c)/2).
The calculator checks the triangle inequality (each side must be shorter than the sum of the other two) and flags invalid combinations.