Perimeter
Key Notes :
π What is Perimeter?
The perimeter is the total distance around a shape.
Think of it as the length of the boundary of a shape.
πΊ Perimeter of a Triangle
Add the lengths of all three sides.
Formula: P = a + b + c
Example: If sides are 3 cm, 4 cm, 5 cm β P = 3 + 4 + 5 = 12 cm β
β¬ Perimeter of a Rectangle
Add all four sides or use the formula:
P = 2 Γ (length + width)
Example: Length = 6 cm, Width = 4 cm β P = 2 Γ (6 + 4) = 20 cm
π© Perimeter of a Square
All sides are equal, so multiply one side by 4.
Formula: P = 4 Γ side
Example: Side = 5 cm β P = 4 Γ 5 = 20 cm
βͺ Perimeter of a Circle
Called circumference.
Formula: C = 2 Γ Ο Γ r or C = Ο Γ d
Example: Radius = 7 cm β C = 2 Γ 3.14 Γ 7 = 43.96 cm
βοΈ Steps to Find Perimeter
Identify the shape.
Note all side lengths.
Use the correct formula.
Add all sides or calculate using the formula.
𧩠Perimeter of Irregular Shapes
Add the lengths of all sides.
Example: A shape with sides 3 cm, 4 cm, 5 cm, 6 cm β P = 18 cm
π‘ Fun Fact:
Perimeter is measured in units like cm, m, km, etc.
It doesnβt depend on the area of the shape.
π¨ Visual Tip:
Imagine walking around the shape β thatβs the perimeter! π£
Learn with an example
βΆοΈ What is the perimeter of the rectangle?
____ centimetres
To find the perimeter, find the total length of the shape’s sides.
Add all of the side lengths.
2 + 1 + 2 + 1 = 6
The perimeter of the rectangle is 6 centimetres. ( Centimetres can be written “cm”.)
βΆοΈ What is the perimeter of the shape?
____ centimetres
To find the perimeter, find the total length of the shape’s sides.
Add all of the side lengths.
2 + 3 + 2 + 3 = 10
The perimeter of the shape is 10 centimetres. ( Centimetres can be written “cm”.)
βΆοΈ What is the perimeter of the rectangle?
_____ centimetres
To find the perimeter, find the total length of the shape’s sides.
Add all of the side lengths.
5 + 6 + 5 + 6 = 22
The perimeter of the rectangle is 22 centimetres. ( Centimetres can be written “cm”.)
Let’s practice!ποΈ
