Perimeter — the distance around
Perimeter is the total length of all sides of a shape.
For a rectangle:
Perimeter = 2 × length + 2 × width (or: add all four sides)
Example: A rectangle 8 cm long and 5 cm wide:
- Perimeter = 2 × 8 + 2 × 5 = 16 + 10 = 26 cm
Think of it as walking all the way around the shape — that’s the perimeter!
Area — the space inside
Area measures how much surface a shape covers. We measure it in square units (cm², m²).
For a rectangle:
Area = length × width
Example: That same 8 cm × 5 cm rectangle:
- Area = 8 × 5 = 40 cm²
Don’t mix them up!
| Perimeter | Area | |
|---|---|---|
| What it measures | Distance around | Space inside |
| Units | cm, m, km | cm², m², km² |
| Rectangle formula | 2(l + w) | l × w |
Identify
Perimeter
Area
Check
Perimeter measures the fence around a garden. Area measures the grass inside it.
Compound shapes
For L-shaped or other compound shapes, split them into rectangles, find each area, then add.
Example: An L-shape made of a 6×4 rectangle and a 3×2 rectangle:
- Area = (6 × 4) + (3 × 2) = 24 + 6 = 30 square units
For perimeter, trace around the outside only.
Practice
A rectangle is 12 cm long and 7 cm wide. What is its perimeter?
Perimeter = 2 × 12 + 2 × 7 = 24 + 14 = 38 cm.
What is the area of that same rectangle (12 cm × 7 cm)?
Area = 12 × 7 = 84 cm².
A square has a perimeter of 36 cm. What is the length of one side?
A square has 4 equal sides. 36 ÷ 4 = 9 cm per side.
A garden is 15 m long and 9 m wide. How much fencing is needed to go all the way around?
Perimeter = 2 × (15 + 9) = 2 × 24 = 48 m.
Which has the greater area: a 10 × 3 rectangle or a 6 × 6 square?
10 × 3 = 30. 6 × 6 = 36. The square has a larger area.
An L-shaped room is made of two rectangles: one 8 m × 5 m and one 4 m × 3 m. What is the total area?
Area = (8 × 5) + (4 × 3) = 40 + 12 = 52 m².
Challenge
Quick-Fire Round