In geometry, Heron's formula (sometimes called Hero's formula), named after Hero of Alexandria, gives the area of a triangle when the length of all three sides are known. Unlike other triangle area formulae, there is no need to calculate angles or other distances in the triangle first. For a quadrilateral, when one of its diagonal value and the sides are given. Then the area can be calculated by splitting the given quadrilateral into two triangles and use the Heron's formula. The Chapter explains essential topics like introduction, Heron's formula and its applications.