Primary 5 Foundation maths · Decimals · About 12 minutes
Convert measurement units using decimals
Write the relationship between the two units and track complete units plus any remainder.
Start the interactive lesson →Open practice activity
What you will learn
- Convert measurement units using decimals
Models used: number sentences, stories, tables.
Before you start
A new unit for the same amount
One m contains 100 cm. We can measure the same amount using either unit.
The complete bar is the whole. Each labelled section is one part of it.
One m contains 100 cm. We can measure the same amount using either unit.
The amount does not grow when we change its name. Smaller units simply need a bigger count.
The complete bar is the whole. Each labelled section is one part of it.
Two m contain two groups of 100 cm.
2 × 100 = 200 cm
First convert the larger-unit part by multiplying by 100.
The complete bar is the whole. Each labelled section is one part of it.
Add another 50 cm. The complete amount is 250 cm.
200 + 50 = 250 cm
The last part is already in small units. Add it after converting the larger units.
Why do we need more small units than large units?
Each small unit measures less, so more of them are needed to describe the same amount.
What did the picture help us see?
Add another 50 cm. The complete amount is 250 cm.
Worked example: A new example, together
Convert 5.6 kg to g.
| Larger unit | Smaller unit |
|---|---|
| 1 kg | 1000 g |
| 5 kg | 5000 g |
The unit changes; the quantity stays the same. Read each value with the heading above its column.
Write the relationship between the two units and track complete units plus any remainder.
Changing units changes the number we count, while the measured amount stays the same.
The unit changes; the quantity stays the same Larger unit Smaller unit 1 kg 1000 g 5 kg 5000 g The unit changes; the quantity stays the same. Read each value with the heading above its column.
1 kg = 1000 g.
The unit changes; the quantity stays the same Larger unit Smaller unit 1 kg 1000 g 5 kg 5000 g Convert 5.6 kg to g.
5600 g
The unit changes; the quantity stays the same. Read each value with the heading above its column.
5 kg = 5000 g.
The unit changes; the quantity stays the same Larger unit Smaller unit 1 kg 1000 g 5 kg 5000 g The unit changes; the quantity stays the same. Read each value with the heading above its column.
5000 + 600 = 5600 g; this is 5.6 kg.
The unit changes; the quantity stays the same Larger unit Smaller unit 1 kg 1000 g 5 kg 5000 g The unit changes; the quantity stays the same. Read each value with the heading above its column.
Check the result against the question we started with.
5600 ÷ 1000 = 5.6 kg.
We found 5600 g. Changing units changes the number we count, while the measured amount stays the same.
The unit changes; the quantity stays the same Larger unit Smaller unit 1 kg 1000 g 5 kg 5000 g
Common mistakes to discuss
- Using one multiplier for every unit. The pairs differ: 100 cm make a metre but 1000 g make a kilogram. So 1 kg 250 g is 1.25 kg, while 3 m 45 cm is 3.45 m.
Check your understanding
- Convert measurement units using decimals
- justify a conversion while preserving the measured quantity
- check the answer against the original quantities and units
Explain your reasoning to an adult, then try a fresh question in the interactive lesson. A result from one attempt is not proof of lasting mastery.
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