Area and Land Measurements
Primary 4 · Mathematics
Area and Land Measurements
Lesson 3 of 5
20 min
Let's begin
Gatete's teacher holds up a square of paper. Each side is 10 cm. "What is its area?" she asks.
"100 cm²!" says Gatete. "Good," says the teacher. "It is also 1 dm²."
How can one square have two answers? Today you will learn the units of area and how to change from one to another.
For every unit of length there is a unit of area: a square with that side.
| Unit of area | A square with sides of |
|---|---|
| square centimetre (cm²) | 1 cm |
| square decimetre (dm²) | 1 dm = 10 cm |
| square metre (m²) | 1 m |
| square decametre (dam²) | 1 dam = 10 m |
| square hectometre (hm²) | 1 hm = 100 m |
| square kilometre (km²) | 1 km = 1 000 m |
A square decimetre is 10 cm long and 10 cm wide. So 1 dm² = 10 × 10 = 100 cm².
Length units jump by 10 at each step. But a square has two sides, so area units jump by 10 × 10 = 100 at each step.
km² → hm² → dam² → m² → dm² → cm²
Careful! 1 m² is not 100 cm². 1 m = 100 cm, so 1 m² = 100 cm × 100 cm = 10 000 cm².
Down the ladder (to a smaller unit): multiply by 100 for each step. Up the ladder (to a bigger unit): divide by 100 for each step.
Worked example 1
5 m² = ? dm². One step down: 5 × 100 = 500 dm².
Worked example 2
3 m² = ? cm². Two steps down: 3 × 100 × 100 = 30 000 cm².
Worked example 3
700 dm² = ? m². One step up: 700 ÷ 100 = 7 m².
Tip
Square units jump by 100. A square has two sides, so each step is 10 × 10 = 100. Going down, multiply by 100. Going up, divide by 100.
Work each one in your exercise book first. Then tap Show answer to check.
4 dm² = ___ cm²
Answer: 400 cm², because 4 × 100 = 400.
6 m² = ___ dm²
Answer: 600 dm².
900 cm² = ___ dm²
Answer: 9 dm², because 900 ÷ 100 = 9.
2 m² = ___ cm²
Answer: 20 000 cm². Two steps down: 2 × 100 × 100 = 20 000.
3 hm² = ___ dam²
Answer: 300 dam².
What you learned today
Sources and credits
The worked examples, drawings, stories and practice questions were written by Ganzaa. Note: that Siyavula page has a misprint. It says to multiply by 1 000 to change m² into cm². The correct number is 10 000, as this lesson shows.
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