Place your tape measure against the wall. Place the tape measure at the leftmost point -- the zero point -- of the line. Apothem Of An Octagon Formulas And Examples Mechamath How do you measure an octagon window. . Correct answer to the question Find the area of the regular octagon if the apothem is 42 and a side is 34 in. The solution to the equation is straightforward and this is the formula used in our regular octagon area calculator. Measure the total number of sides. Since we know that the octagon is regular and we know the apothem height from a side to the center of the polygon we can calculate the side length. To find the formula for the apothem we can use the diagram of a pentagon. A hexagon has 6 sides. Finally calculate the apothem. First determine the number of sides. Each angle of the central angle. Area of the octagon is calculated by summing up the areas of the 8 triangles or...