The idea, step by step
Use the unit relationship
One metre is 100 centimetres; one kilometre is 1,000 metres. One kilogram is 1,000 grams, and one litre is 1,000 millilitres. A measurement changes its number when its unit changes, but the actual amount stays the same.
A smaller unit needs a larger count. To convert 2.4 metres to centimetres, use 2.4×100=240. To convert 650 millilitres to litres, use 650÷1,000=0.65.
| Larger unit | Equivalent smaller units |
|---|---|
| 1 m | 100 cm |
| 1 km | 1,000 m |
| 1 kg | 1,000 g |
| 1 L | 1,000 mL |
Check the direction
Before calculating, predict whether the number should increase or decrease. Changing kilograms to grams gives a larger number because each gram is smaller. If 3.2 kilograms became 0.0032 grams, that would clearly not be the same mass.
Write units at every stage. Do not use the same conversion factor for every pair: metres to centimetres uses 100, while metres to millimetres uses 1,000.
A common trap
Every metric conversion means moving the digits three places.
Instead: First identify the actual units. Metres to centimetres uses a factor of 100, not 1,000.
See the thinking
Worked example 1
Convert 1.75 metres to centimetres.
- There are 100 centimetres in one metre.
- 1.75×100=175.
Worked example 2
Convert 2,450 grams to kilograms.
- There are 1,000 grams in one kilogram.
- 2,450÷1,000=2.45.
Check your understanding
Convert 0.6 litres to millilitres.
Show answer
600 mL.
0.6×1,000=600. The smaller unit needs a larger count.
Your turn
6 questions · 7 marks · Work at your own pace.
Read the questions online
- Convert 3.25 m to centimetres.1 mark
- Convert 740 cm to metres.1 mark
- Convert 0.85 kg to grams.1 mark
- Convert 1,250 mL to litres.1 mark
- A walk is 2.3 km. How many metres is that?1 mark
- A learner writes 4.2 m=42 cm. Explain the error and correct it.2 marks
Read the worked solutions
Equivalent correct methods earn the corresponding marks. Include units where asked.
- Convert 3.25 m to centimetres.1 mark
3.25×100=325.
325 cm. - Convert 740 cm to metres.1 mark
740÷100=7.4.
7.4 m. - Convert 0.85 kg to grams.1 mark
0.85×1,000=850.
850 g. - Convert 1,250 mL to litres.1 mark
1,250÷1,000=1.25.
1.25 L. - A walk is 2.3 km. How many metres is that?1 mark
2.3×1,000=2,300.
2,300 m. - A learner writes 4.2 m=42 cm. Explain the error and correct it.2 marks
Each metre contains 100 centimetres, not 10.
4.2 m=420 cm.
Curriculum reference & lesson scope
Australian Curriculum v9 and SA Curriculum Mathematics
Decimal metric conversions; deriving rectangle area; missing dimensions; practical measurement.
Official curriculum source ↗