Perimeter
What does it mean?

Let’s find the perimeter.
8 ft
10 ft
12 ft

Let’s find the perimeter.
15 in
20 in 20 in
10 in

Let’s find the perimeter.
This is a regular polygon.
What is a regular polygon?
A regular polygon is one in which all sides are the same length.
So, if one of this polygon’s sides measures 5 cm...
…what would the perimeter of this polygon be?

Let’s find the perimeter.
5 cm
5 cm
5 cm
5 cm
5 cm
5 cm
5 cm
5 cm
5 cm
5 cm

So, how would you find the perimeter of this rectangle?
length
???

width
So, how would you find the perimeter of this rectangle?
length
???
length

width
So, how would you find the perimeter of this rectangle?
length width length

width
So, how would you find the perimeter of this rectangle?
length length + length + width + width =
2 x length + 2 x width =
2l + 2w = width length

So, how would you find the perimeter of this rectangle?
7 mm
???

So, how would you find the perimeter of this rectangle?
7 mm
???
5 mm
7 mm

So, how would you find the perimeter of this rectangle?
5 mm
7 mm
2l + 2w =
2 x 7 + 2 x 5 =
14 + 10 =
5 mm
7 mm

8 ft
Find the Perimeter
10 ft
2l + 2w =
2 x 10 + 2 x 8 = 0
20 + 16 =
8 ft
10 ft

7 in
Find the Perimeter
3 in
2l + 2w =
2 x 7 + 2 x 3 =
14 + 6 =
???
???

6 in
Rectangle Perimeter Formula
2 in
2l + 2w = perimeter of a rectangle
2 x length + 2 x width
2l + 2w =
2 x 6 + 2 x 2 =
12 + 2 x 2 =
12 + 4 =

Find the Perimeter
Use: 2l + 2w = perimeter of a rectangle
1 yds
Step 1: Write the formula.
Step 2: Replace the variables.
Step 3: Multiply first.
Step 4: Add last.
Step 5: Write the answer with the correct units.
10 yds
2l + 2w =
2 x 10 + 2 x 1 =
20 + 2 =
20 + 2 = 22
22 yds

Find the Perimeter
Use: 2l + 2w = perimeter of a rectangle
9 in
3 in
Step 1: Write the formula.
Step 2: Replace the variables.
Step 3: Multiply first.
Step 4: Add last.
Step 5: Write the answer with the correct units.
2l + 2w =
2 x 9 + 2 x 3 =
18 + 6 =
18 + 6 = 24
24 in

Try one with someone at your table.
Use: 2l + 2w = perimeter of a rectangle
4 cm
8 cm
Step 1: Write the formula.
Step 2: Replace the variables.
Step 3: Multiply first.
Step 4: Add last.
Step 5: Write the answer with the correct units.
2l + 2w =
2 x 8 + 2 x 4 =
16 + 8 =
16 + 8 = 24
24 cm

side
So, how would you find the perimeter of this square?
side side side

side
So, how would you find the perimeter of this square?
side side + side + side + side = side
4 x side =
4s = side

7 mm
So, how would you find the perimeter of this square?
7 mm 4s =
4 x 7 =
7 mm
7 mm

5 ft
So, how would you find the perimeter of this square?
5 ft
4s =
4 x 5 =
5 ft
5 ft

Square Perimeter Formula
3 in
4s = perimeter of a square
4 x side
4s =
4 x 3 =

Find the Perimeter
Use: 4s = perimeter of a square
10 yds
Step 1: Write the formula.
Step 2: Replace the variables.
Step 3: Multiply and write the correct units in your answer.
4s =
4 x 10 =
4 x 10 = 40 yds

Find the Perimeter
Use: 4s = perimeter of a square
9 cm
Step 1: Write the formula.
Step 2: Replace the variables.
Step 3: Multiply and write the correct units in your answer.
4s =
4 x 9 =
4 x 9 = 36 cm

Try one with someone at your table.
Use: 4s = perimeter of a square
6 mm
Step 1: Write the formula.
Step 2: Replace the variables.
Step 3: Multiply and write the correct units in your answer.
4s =
4 x 6 =
4 x 6 = 24 mm

Let’s Review
What does perimeter mean?
•
Perimeter is the distance around the edge of an object.
What is the formula for finding the perimeter of a rectangle?
What is the formula for finding the perimeter of a square?

Now it is your turn.