Determine the shape you want to measure. Perimeter is the outside boundary around a closed geometric figure, and different shapes will require different approaches. If the shape that you want to find the perimeter of is not a closed shape, the perimeter cannot be taken.
If this is the first time you are calculating perimeter, try a rectangle or a square. These regular shapes will make finding the perimeter easier.

2
Draw a rectangle on a piece of paper. You will use this rectangle as a practice shape and will find its perimeter. Make sure that the opposite sides of your rectangle are the same length.[4]

3
Find the length of one side of your rectangle. You can do this with a ruler, measuring tape, or by making up your own example. Write down this number by the side it represents so you don't forget its length. As a guided example, imagine that the length of one side of your rectangle is 3 feet.
For small shapes you may want to use centimeters or inches, while feet, meters or miles will work better for larger perimeters.
Since the opposite sides of rectangles are equal, you will only have to measure one of each set of opposing sides.[5]

4
Find the width of one side of your rectangle. You can measure the width with a ruler, measuring tape, or by creating your own example. Write down the value for your width next to the horizontal side of your rectangle it represents.
Continuing with the guided example, imagine that in addition to a length of 3 feet, that the width of your rectangle is 5 feet.

5
Write down the correct measurements on the opposing sides of your rectangle. Rectangles have four sides, but the length of opposite sides will be the same.[6] This is also true for your rectangle's width. Add the length and width used in the guided example (3 feet and 5 feet respectively) to the opposite sides of your rectangle.

6
Add all your sides together. One a piece of scratch paper, or on the paper you have written the guided example, write: length + length + width + width.[7]
So, for the guided example, you would add 3 + 3 + 5 + 5 to get a perimeter of 16 feet (4.9 m).[8]
You can also use the formula 2(length + width) for rectangles, since the length and width values are doubled. In our example you would multiply 2 by 8 to get 16 feet (4.9 m).
