Measure length — millimetres, metres, kilometres
A clear starting point, worked steps and space to practise.
Start here
Compare lengths using the same unit. Each conversion follows a fixed relationship.
For a bigger unit to a smaller unit, the number grows: 2 m becomes 200 cm.
1 Work through these steps
- Choose one common length unit.
- Use 10 mm = 1 cm, 100 cm = 1 m or 1,000 m = 1 km.
- Convert both lengths.
- Compare or calculate, then write the unit.
2 Follow a worked example
Which is longer: 1 m 25 cm or 118 cm?
- 1 m 25 cm = 125 cm.
- 125 cm is greater than 118 cm.
- The first length is longer by 7 cm.
3 Try it yourself
Show each step on paper or open Working out. Then check the answer.
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Convert 3.2 km to metres.
Check answer 1
Answer: 3,200 m
1 km = 1,000 m, so 3.2 × 1,000 = 3,200.
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Working out
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Check your understanding
Explain the worked example in your own words. Say why the method works, not just what the answer is.
Skills and explanation links
Key ideas taught here
- Compare lengths using the same unit. Each conversion follows a fixed relationship.
- For a bigger unit to a smaller unit, the number grows: 2 m becomes 200 cm.
Method and checking
Optional recap: related Maths skills
These earlier examples revisit background skills. Start with the topic example and practice above.
Useful vocabulary
- length
- How long, wide or tall something is.
- mass
- How heavy something is.
- capacity
- How much a container can hold.
- scale
- A set of marks that shows measured values, such as on a ruler, thermometer or map.
Rules for these related skills
Length, mass, capacity, temperature and distance use different tools and units.
Use mm, cm, m and km for length; g and kg for mass; mL and L for capacity; °C for temperature.
Check what each tick mark represents before reading a ruler, thermometer, jug, scale or map.
Which is longer: 120 cm or 1 m?
- 1 m = 100 cm.
- 120 cm is greater than 100 cm.
- 120 cm is longer.
Convert 3 m to centimetres.
- 1 m = 100 cm.
- 3 x 100 = 300.
- 3 m = 300 cm.
Which is shorter: 900 mm or 1 m?
- 1 m = 1000 mm.
- 900 mm is less than 1000 mm.
- 900 mm is shorter.
A ribbon is 2 m long. Ava cuts off 75 cm. How much is left in centimetres?
- 2 m = 200 cm.
- 200 cm - 75 cm = 125 cm.
- 125 cm is left.
More visual models and everyday examples
Each everyday example has its own information and model. Use its stated values rather than copying values from another question.
Concept example. The story examples below have their own diagrams.
Choose the attribute first: length, mass, capacity, temperature or distance.
For parents and teachers
- Ask your child to explain the method aloud before writing the answer.
- Use a real-life context at home, such as shopping, cooking, sport scores, maps or timetables.
- Praise clear working and checking, not only speed.
- Encourage a quick diagram or table for word problems before calculating.
Practise choosing a method from the information in the question. The examples here are Pi Leo Academy learning activities. Official NAPLAN testing takes place in Years 3, 5, 7 and 9; a topic appearing in these notes does not mean it is tested in NAPLAN.
These notes provide guided examples and practice; they do not certify completion of every curriculum requirement.