Perimeter is the sum of the sides of a two-dimensional shape. To calculate the perimeter of square, you have to sum the 4 sides. In this scenario, perimeter is already provided. To calculate how long each side is, you just have to divide 52 by 4 because square has 4 equal sides. 52 by 4 is 13. Therefore, each side of the confetti measures 13 millimeters.