What is the length of a diagonal of a square is 10√2 inches? Find the length of one side of the square.

Multiply the side length by 4 to find the perimeter. Take the length of the L side you just calculated and connect it to the perimeter formula, P = 4L. The result will be the perimeter of the square! For a square with an area of 20 and a side length of 4,472, the perimeter P = 4 * 4,472 or 17,888.