Octagon is a two-dimensional shape connected together using the straight lines. By the octagon area formula, to find the area, it's important to know the length of any one side, as regular octagon have the same length all the sides. Using area of an octagon equation, square the side length and multiply it with 2. On the other end, find (1+ √(2)). Add both the values to know the octagonal area. You can use our online octagonal area calculator to find the area.