**Introduction to The Perimeter of Noncircular Shapes**

*With me everything turns into mathematics*.

—Renè Descartes (1596–1650)

This lesson will describe ways that geometry is used for measuring, specifically perimeter. Perimeter has many uses in real life outside of your math classroom.

**When you measure** the distance around a noncircular shape, you are finding its perimeter.

Perimeter is an addition concept; it is a linear, one-dimensional measurement.

To find the perimeter of a noncircular shape, add up all of the lengths of the sides of the figure. Be sure to name the units.

The perimeter of a **square**, or any rhombus, is equal to 4*s*, where *s* is the length of a side. Because all four sides are equal, when you measure the distance around a square, you get *s* + *s* + *s* + *s*, or 4*s*.

In a rectangle, like all parallelograms, the opposite sides are parallel and congruent. The perimeter of a **rectangle** is 2*l* + 2*w*, where *l* equals the length and *w* equals the width. Always remember that the length is longer.

To find the perimeter of a triangle, you just add up the lengths of all three sides:

Let's practice!

Find the perimeter of a square whose side is 5 cm.

You know that each side of a square is equal. So, if you know that one side of a square is 5 cm, then you know that each side of the square is 5 cm. To calculate the perimeter, add up the lengths of all four sides.

- 5 + 5 + 5 + 5 = 20

So, the perimeter of a square whose side measures 5 cm is 20 cm.

## Tip:Be alert when you work with geometry problems to make sure that the units are consistent. If they are different, you must make a conversion before calculating perimeter or area. |

Find practice problems and solutions at The Perimeter of Noncircular Shapes Practice Questions.

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