If the shape's measurements are not given, you'll need to measure by hand. Unless otherwise indicated, plan to measure in inches. In the case of a square, measure any one side, and for a rectangle measure both the length and width. Record these measurements on a piece of paper.
In order to determine the perimeter of a square, use the following formula: 4(s) = P. S refers to the length of one side, and P refers to perimeter. If the length of one side is 3, then the perimeter is 3 multiplied by 4 which equals 12.
In order to determine the perimeter of a rectangle, use the following formula: 2(L) + 2(W) = P. L refers to the length of the rectangle and W refers to the width. If the length is 3 and the width is 4, than the perimeter is 2 multiplied by 3, plus 2 multiplied by 4, which equals 6 plus 8, or 14.