# Heron's Formula **Heron's formula** is for calculating the [[area of a triangle]] in terms of its side-lengths alone. For a triangle with side lengths $a$, $b$, and $c$ define the _semi-perimeter_ to be half of its perimeter: $$ s = \frac{a + b + c}{2} $$ Then the area of this triangle is: $$ A = \sqrt{s (s - a) ( s - b) (s - c)} $$ category: triangles