Area of Shapes in the Plane
Primary 4 · Mathematics
Area of Shapes in the Plane
Lesson 1 of 5
30 min
Let's begin
Mutesi's class is getting new floor mats. "How many square mats do we need to cover the whole floor?" asks the teacher. Mutesi says, "Let's count how many fit along the wall, and how many rows there are."
The amount of flat surface a shape covers is its area. Today you will find the area of rectangles.
We measure area by counting how many unit squares cover a shape, with no gaps and no overlaps.
A geoboard is a board with pegs in rows. You stretch a rubber band round the pegs to make shapes. The space between four pegs is one unit square.
This rectangle has 3 rows with 5 squares in each row. You could count 1, 2, 3 … 15. A quicker way is to multiply: 3 × 5 = 15. The area is 15 square units.
Area of a rectangle = length × width
Example: a classroom floor is 8 m long and 6 m wide. Area = 8 × 6 = 48 m². So 48 mats of 1 m² would cover it.
The perimeter is the distance around a shape. The area is the space inside it. For the 5 by 3 rectangle, the perimeter is 5 + 3 + 5 + 3 = 16 units, but the area is 15 square units.
Open the Area Builder simulation and choose Explore. Drag unit squares to build rectangles, then check the area it shows against length × width.
Tip
Rows times squares in a row. Area = length × width, and the answer is always in square units: cm² or m².
Work each one in your exercise book first. Then tap Show answer to check.
A rectangle on a geoboard is 4 units long and 2 units wide. What is its area?
Answer: 8 square units, because 4 × 2 = 8.
A school garden bed is 7 m long and 3 m wide. Find its area.
Answer: 21 m², because 7 × 3 = 21.
An exercise-book cover is 20 cm long and 15 cm wide. Find its area.
Answer: 300 cm², because 20 × 15 = 300.
A rectangle is 6 cm long and 2 cm wide. Find its perimeter AND its area.
Answer: Perimeter 16 cm (6 + 2 + 6 + 2). Area 12 cm² (6 × 2).
A rectangle has an area of 24 m² and a length of 6 m. How wide is it?
Answer: 4 m, because 6 × 4 = 24.
What you learned today
Sources and credits
The stories, Rwandan examples, diagrams and practice questions were written by Ganzaa.
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