Area & perimeter
Area and perimeter of rectangles
For a rectangle we can calculate the area by multiplying the length by the width, and the perimeter by adding all four sides. When a floor is made of two rectangles, we add their areas together.
Area of a rectangle
The area of a rectangle = length × width. You can also count the squares: if a rectangle has 3 squares in each column, count in 3s. Both give the same answer. Area is measured in square units like cm² and m².
Perimeter of a rectangle
The perimeter is the distance all the way around. Add every side: length + width + length + width. Because opposite sides are equal, you can also add the length and width and double the total.
Adding areas together
Some shapes, like an L-shaped floor, are made of two rectangles joined together. Find the area of each rectangle, then add the areas to find the total area.
Worked examples
Area of a rectangle
- The rectangle is 4 cm long and 3 cm wide.
- Area = length × width = 4 × 3.
- Or count 3 squares in each of the 4 columns: 3, 6, 9, 12.
Answer: The area is 12 cm².
Perimeter of a rectangle
- The rectangle has sides 3 cm, 4 cm, 3 cm and 4 cm.
- Add every side: 3 + 4 + 3 + 4.
Answer: The perimeter is 14 cm.
Adding two rectangle areas
- A hall is 4 m × 3 m = 12 m².
- A main office is 6 m × 9 m = 54 m².
- Add the areas: 12 + 54.
Answer: The total floor area is 66 m².
Where you see this in real life
- Working out how much floor covering to buy for a rectangular room.
- Finding the total area of a building made from two rectangular rooms.
- Measuring how much fencing goes around a rectangular garden (perimeter).
- Buying tiles by the square metre to cover a rectangular wall.
Key words
- Area
- The amount of surface a shape covers; for a rectangle, length × width.
- Perimeter
- The total distance around the edge of a shape.
- Length
- How long the longer side of a rectangle is.
- Width
- How wide the shorter side of a rectangle is.