Ans: An octagon having eight equal sides is called a regular octagon. There are some particular formulas for the measurement of a regular octagon. If the length of the sides of the regular octagon is a, the area of the octagon is 2a2(1+√2). The perimeter of the regular octagon is equal to the sum of all the sides, which is 8a. By joining the opposite vertices of the regular octagon, we will get the diagonals of the octagon. A regular octagon has 20 diagonals and their lengths are equal. The length of the diagonal of a regular octagon is a√(4 + 2√2). These are the primary measurement formulas of a regular octagon.