Perimeter

 

What is Perimeter?

Perimeter is the total distance around the outside of a 2D shape.
The perimeter of a circle is called the circumference.
Perimeter is measured in length units such as mm, cm, m, or km.

Example:

• A square with side length 5 cm has a perimeter of: $$4 \times 5 = 20 cm$$

 

How to Find the Perimeter of a 2D Shape

To calculate the perimeter, add up the lengths of all sides.

For regular shapes:

• Use Perimeter = (number of sides) × (side length)

For irregular shapes:

• Add the lengths of all individual sides.

Example: Perimeter of a Rectangle

• A rectangle has a length of 10 cm and a width of 4 cm. $$\text{Perimeter} = 2(10 + 4) = 2(14) = 28 cm$$

 

Final Answer: 28 cm.

 

Perimeter of Compound Shapes

A compound shape is made up of two or more basic 2D shapes.

Steps to Find the Perimeter of a Compound Shape:

1. Break the shape into smaller known shapes (rectangles, triangles, circles, etc.).

2. Find missing side lengths using properties of shapes (e.g., parallel sides in rectangles).

3. Sum all outer sides to get the total perimeter.

 

 

 

Example: Find the Perimeter of the Shape Below

 

 

• Shape consists of two rectangles and an equilateral triangle.

• Given side lengths: 9 cm, 3 cm, 6 cm, 4 cm,  4 cm, 5 cm.

• Perimeter Calculation: $$9 + 3 + 6 + 4 + 4 + 5 + 16 + 6 = 53 cm$$

   

Final Answer: 53 cm.