Learn the idea
Perimeter measures the boundary. A rectangle has two sides of each length, so you can add all four sides or double the sum of length and width.
- Identify the length and width in the same unit.
- Add length + width + length + width.
- Label the result with a length unit.
LET’S WORK IT OUT
Worked example
A rectangle is 8 cm long and 3 cm wide. Find its perimeter.
8 + 3 + 8 + 3 = 22 cm
The opposite sides match. The full boundary is twice 8 + 3.
A mistake to watch for
Length × width gives area. Perimeter is a distance, so use cm rather than square cm.
YOUR TURN
Try three practice questions
Enter your answer, then check the explanation. You can also open each explanation to study it. These three questions check understanding; they are not a mastery score.
Question 1
A rectangle is 6 cm by 4 cm. Enter its perimeter in cm.
Answer and explanation
20 — 6 + 4 + 6 + 4 = 20.
Question 2
A rectangle is 9 m by 2 m. Enter its perimeter in m.
Answer and explanation
22 — Twice 9 + 2 is 22.
Question 3
A square has side length 5 cm. Enter its perimeter in cm.
Answer and explanation
20 — All four sides measure five; 4 × 5 = 20.
For parents and teachers
Trace a rectangle with a finger before calculating its boundary.
Ask your learner to explain the method before moving on. This lesson covers one focused skill and is not a complete curriculum assessment.