Maths · KS3 and GCSE · Interactive lesson
Converting units: length, mass, time, area and volume
Change the unit without changing the measurement. Start with length, mass and time, then learn why area and volume need different factors.
Choose your view
Explore an interactive example, then try the questions at your own pace.
KS3 / GCSE · start with the idea
By the end of this lesson: Change the unit without changing the size of a measurement.
The interactive diagram and controls are in Stage 2, “Explore one example”. Read the idea here, then try it next.
- A metre and a centimetre measure the same kind of thing: length.
- A larger unit contains more smaller units. One metre contains 100 centimetres.
- The measurement stays the same; only the unit and its number change.
Useful starting points
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What do the words mean?
- Unit
- An agreed size used for measuring, such as a metre or a second.
- Square unit (²)
- Measures area: two lengths multiplied together.
- Cubic unit (³)
- Measures volume: three lengths multiplied together.
Change the example
This is the lesson example. Your practice question uses its own numbers.
Something to try
Convert one measurement. Is the new unit smaller or larger? Predict whether you need more or fewer of those units.
Notice what changes
How particle motion works +
Starts paused. Press Play, then add energy to see the warmer particles move faster.
Particles keep the same size. Liquid particles move around; solid particles vibrate around fixed positions. This is a simplified model, with the change in motion exaggerated to make it easier to see.
About the playback +
About this model
The bars show a reference size: 1 metre = 100 centimetres. Each lower block represents 10 centimetres. The measurement does not change when its unit changes. ≈ marks a rounded display value.
More about this diagram
Still picture. Play particle motion in Stage 2.
250 cm = 2.5 m
Still picture of the example from Stage 2. Use the back arrow to change it.
Work through it
Starting example: read the steps below
- We have 250 cm and want m.
- Use this fact: 1 metre = 100 centimetres.
- The target unit is larger, so the number becomes smaller. Divide by 100.
- 250 ÷ 100 = 2.5 m.
Try on your own
Your turn. No rush.
Question 1
Convert 250 cm to metres.
About these questions
Questions appear in a mixed order. Work at your own pace and stop whenever you like.
These questions use their own numbers, separate from the lesson example. You can stop whenever you like. Answers last for this visit to the page.
A good place to pause
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Can you choose a conversion factor and say why the number gets bigger or smaller?
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Useful starting points
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Notes for parents and tutors
These lessons cover selected KS3 and GCSE ideas for England; they are not a complete course. The level notes explain where GCSE methods or optional extensions begin. Maurice can help you choose material for your course and exam board.
The content draws on the DfE Maths curriculum, DfE Science curriculum and AQA GCSE Physics specification. Level labels are guidance, not exam-board endorsements. For AQA Radioactivity, calculating net decline as a ratio is Higher-tier work. Net means the overall change; ask Maurice whether this extension is relevant to your course. Explanations and practice were reviewed during development on 21 October 2026; Maurice should check their fit before assigning work.
Topic labels and your lesson-view preference are saved in this browser. This tab also remembers the last lesson stage, so you can choose to continue there. If you choose revision, selected activities and suggested revisit dates are saved here too. Recent question codes are also kept to reduce repeats. Reflection notes are saved automatically per topic when you type them; you can delete a note in the recap. They stay in this browser and are visible to other people using it. Practice answers and enquiry details are not saved. Clearing browser data removes the labels.