Perimeter

Definition

Definition Perimeter

The perimeter of a shape is the total length around its outside edge.

To find the perimeter, imagine walking around the shape like it’s a park. Count the number of unit lengths along each side as you go.

Example

Find the perimeter of the red shape:

Answer

To find the perimeter, we add the length of all 4 sides : 2 + 2 + 2 + 2.
The perimeter is 8 units.

Perimeter of Common Shapes

Method Finding a Polygon’s Perimeter

To find the perimeter of any polygon (a shape with straight sides), add up the lengths of all its sides.

Proposition Perimeter Formulas

Name	Shape	Perimeter
Triangle		$a + b + c$
Rectangle		$l+w+l+w= (2\times l) + (2\times w) $
Square		$s+s+s+s=4\times s$

Example

Find the perimeter of the rectangle:

Answer

This is a rectangle with length $l = 14$ m and width $w = 7$ m. Using the formula for the perimeter of a rectangle:$$\begin{aligned}[t]P &= (2\times l) + (2\times w) \\ &= (2 \times 14) + (2 \times 7) \\ &= 28 + 14 \\ &= 42 \, \mathrm{m}\end{aligned}$$So, the perimeter is $42$ meters.