## Finding Perimeter and Circumference

**Perimeter** is the distance around the outside of a two-dimensional shape.

For shapes made up of straight lines, the perimeter is found by adding the lengths of the sides. If the shape is a square, the perimeter is four times the length of one side (P = 4*l*). If the shape is a rectangle, you can use this formula: P = 2(*l* × *w*). For irregular polygons, the best way to find the perimeter is simply to add the lengths of all the sides. As an example, a triangle with sides of 3, 4, and 5 inches would have a perimeter of 12 inches.

Perimeter is expressed in units of length: in other words, not in square units like those we use for area, and not in cube units like those we use for volume.

The perimeter of a circle is more commonly called the **circumference**.

All of these formulas are on the reference sheet you will be given on the day of the test.