Perimeter
Key Notes :
π‘ The perimeter of a shape is the distance around the shape. It is the total length of the shape’s sides.
What is the perimeter?
Perimeter is the distance around the outside of a two-dimensional shape. The perimeter of a shape is the total length of the shape’s sides. Perimeter is measured in units such as centimeters, inches, feet, yards, meters, kilometers, and miles.
π£Calculating Perimeter: To find the perimeter of a polygon, add together the lengths of all its sides
Formulas:
- Square: Perimeter = 4 Γ side length
- Rectangle: Perimeter = 2 Γ (length + width)
- Triangle: Perimeter = sum of the lengths of all three sides
Let’s try it!
π΄ The perimeter of this triangle is highlighted.
To find the perimeter, add the lengths of all three sides.
3+4+5=12
So, the perimeter is 12 centimeters!
π΄ The perimeter of the rectangle is highlighted.
To find the perimeter, add the lengths of all four sides.
2+5+2+5=14
So, the perimeter is 14 centimeters!
π΄Perimeter formula for rectangles
You can use multiplication to find the perimeter of rectangles and regular polygons.
To find the perimeter of a rectangle, use this formula, where β is the length of the rectangle and w is the width:
P=(2Γβ)+(2Γw)
Let’s try it!
P=(2Γ4)+(2Γ6)
P=8+12
P=20
So, the perimeter is 20 feet!
π΄Perimeter formula for regular polygons
A regular polygon is a shape where all the sides are the same length. To find the perimeter of any regular polygon, use this formula, where n is the number of sides and s is the side length:
P=nΓs
Let’s try it!
This shape is a regular octagon. An octagon has 8 sides, so n=8.
P=8Γ2
P=16
So, the perimeter is 16 inches!
π§ΏThe perimeter of a circle
The perimeter of a circle has a special name. It’s called the circumference.
To find the circumference of a circle, use this formula, where r is the radius:
C=2ΓβπΓr
Let’s try it!
C= 2ΓβπΓ4
C= 8Γβπ
If we use 3.14 for βπ, the circumference is about 25.12 meters!
Learn with an example
π΄ What is the perimeter of the rectangle?
π₯ To find the perimeter, find the total length of the shape’s sides.
Add all of the side lengths.
6 + 4 + 6 + 4 = 20
The perimeter of the rectangle is 20 meters. (Metres can be written “m”.)
π΄ What is the perimeter of the shape?
π₯ To find the perimeter, find the total length of the shape’s sides.
Add all of the side lengths.
1 + 7 + 4 + 3 + 5 = 20
The perimeter of the shape is 20 centimeters. (Centimetres can be written “cm”.)
Let’s practice!ποΈ