Rectangle perimeter
A rectangle with sides 8 cm and 5 cm has a perimeter of 26 cm.
Go right around the outside.
Year 4
Measure and calculate the perimeter of a rectilinear figure in centimetres and metres
Find the perimeter of rectilinear figures by adding all the outer side lengths carefully.
Lesson overview
Measurement
Perimeter is the total distance around the outside of a shape. A rectilinear figure has straight sides that meet at right angles. To find the perimeter, add all the outer sides once.
Rectilinear figures still use the outside edge
Even when the shape turns corners, perimeter still means around the outside.
Trace the outside in your mind.
Use the correct unit
A smaller figure might use centimetres while a larger one might use metres.
Keep the unit in the final answer.
Worked example
Find the perimeter of a rectilinear figure with side lengths 6 m, 2 m, 4 m and 8 m.
- List each outside side length once.
- Add the side lengths together carefully.
- 6 + 2 + 4 + 8 = 20.
- So the perimeter is 20 m.
Round 1: Learn it
Follow the outside edge of the figure and include every side once.
Finish this round to unlock Round 2: Show you know it.
Question 1
What is the perimeter of a rectangle with sides 7 cm and 4 cm?
Question 2
What is the perimeter of a figure with side lengths 3 m, 5 m, 3 m and 5 m?
Question 3
A figure has outside side lengths 9 cm, 2 cm, 9 cm and 2 cm. What is its perimeter?
Question 4
Which word means the distance around a shape?
Question 5
What must you add to find perimeter?
all outside sides
corners only
Common mistakes
Watch for these as you work through the lesson.
- Missing one side when adding.
- Adding across the shape instead of around the outside.
- Leaving the unit out of the final answer.
Related topics
These ideas connect closely to this lesson.
- Convert between different units of measure.
- Find the area of rectilinear shapes by counting squares.