Checks triangle inequality.
Heron’s formula with semiperimeter s = (a+b+c)/2 and area √(s(s−a)(s−b)(s−c)). All sides must be positive and satisfy the triangle inequality. If the radicand is negative due to numerical edge cases, the tool reports an error.
This calculator uses plain decimal numbers. If a result looks wrong, check whether you used a comma instead of a dot (or vice versa) where the field expects one.