To find the perimeter of a square, just add up all the lengths of the sides: The area of a square: To find the area of a square, multiply the lengths of two sides together... Another way to say this is to say "square the length of a side!" and for the rectangle, The perimeter is the length of the outline of a shape. To find the perimeter of a rectangle or square you have to add the lengths of all the four sides. x is in this case the length of the rectangle while y is the width of the rectangle.