Perimeter is the distance all the way round the outside of a shape.
Perimeter is the total distance around the edge of a shape.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
Add every side
Walk round the shape and add each side as you pass it.
A rectangle shortcut
A rectangle has two of each side. So perimeter is width + height + width + height.
Not square units
A perimeter is a length, so it is measured in units, not square units.
Perimeter is the distance round the edge
Perimeter is what you would walk if you went all the way around the outside of a shape and back to your starting point. It is a length, so it is measured in centimetres or metres — not in square units.
Add every side
For a rectangle 6 by 4, the perimeter is 6 + 4 + 6 + 4 = 20. Some people use 2 × (6 + 4), which is the same thing grouped differently. For an irregular shape there is no formula — you simply add all the sides, so mark each one as you use it.
Missing sides on a drawing
Diagrams often leave some side lengths off, expecting you to work them out from the opposite sides. On a rectangle, opposite sides are equal, so one measurement gives you two. Fill in every side on the drawing before adding anything.
Step 2: Try It Yourself
Tap and try it out.
Area · squares inside
15
Perimeter · walk around
16
5 × 3 = 15 · 5 + 3 + 5 + 3 = 16
Area counts the squares inside. Perimeter measures the walk all the way round.
Step 3: Watch an Example
One step at a time.
Watch Ana Walk the Edge
Ana finds the perimeter of a rectangle 5 by 3.
- Step 1
She starts at a corner and walks along the top: 5.
Step 4: Your Turn
Practice makes it stick.
The Fence
Problem 1 of 2
A garden is 8 m by 6 m. How much fence goes all the way round?
metres
The Picture Frame
Problem 2 of 2
A frame is 9 cm by 4 cm. What is its perimeter?
cm
Add the Sides
1 of 3
A rectangle 7 by 3. What is its perimeter?
2 of 3
A square with sides of 6. What is its perimeter?
3 of 3
A rectangle 10 by 2. What is its perimeter?
Step 5: Quick Check
Show what you know.
Question 1 of 2
A rectangle 9 by 5. What is its perimeter?
Question 2 of 2
What units does a perimeter use?
What You Learned
- Perimeter is the distance all the way round.
- Add every side of the shape.
- It is a length, so no square units.