what is the size of each interior angle in a regular octagon?

180(8-2) = 180*6

135, because the sum of all interior angles in polygon increase with 180 degrees as each side is added. e.g. triangle is 180, quadrilateral (like square) is 360, pentagon is 540, hexagonis 720, septagon is 900, and octagon is 1080. therefore 1080/8 = 135

360/8 just divide and you get your answer.