Understand the idea.
Three kinds of measurement
Before choosing a unit, decide what you are measuring. Length describes how long or how far: a pencil suits centimetres, while a classroom suits metres. The larger unit avoids counting a very large number of tiny steps.
Mass describes how heavy an object is. Grams suit a small object such as an apple. Kilograms suit heavier objects such as a full school bag. Use scales rather than a ruler to measure mass.
Choose a unit that fits
Capacity describes how much a container can hold. Millilitres suit a small drink carton; litres suit a larger bottle or bucket. A measuring jug helps you read a liquid amount.
Write the unit beside every measurement. A number alone does not tell the size or even what was measured. Two litres and two millilitres have the same number but describe very different capacities.
| What to measure | Useful tool | Possible unit |
|---|---|---|
| Ribbon length | Ruler | cm |
| Mass of fruit | Scales | g |
| Water in a jug | Measuring jug | mL |
See the method in action.
A classroom
Choose centimetres or metres for a classroom length.
Worked solution
- 1
Identify the measurement.
The distance from one end of a classroom to the other is a length.
- 2
Compare the size with a familiar object.
A classroom is much longer than a pencil, so centimetres would give a large count.
- 3
Choose metres, written m.
Metres are a convenient unit for a room-sized length; no exact room measurement is supplied.
Metres (m).
A small juice carton
Which label fits one small juice carton: 200 mL or 200 L?
Worked solution
- 1
Identify what the label measures.
A juice carton holds liquid, so the label describes capacity.
- 2
Compare the two units with the carton.
Millilitres suit a small drink; 200 litres would require a much larger container.
- 3
Select the small-drink label.
This amount is a sensible capacity for one small juice carton.
200 mL.
Try it yourself.
Check your understanding
Which unit fits the mass of an apple: g, m or L?
Show answer & reasoning
g
The answer is g, for grams. The question asks about mass, so neither metres, which measure length, nor litres, which measure capacity, fits.
Keep practising
6 worksheet questions
Read the questions online
- Choose cm or m for a pencil length.
- Choose g or kg for the mass of a child.
- Choose mL or L for the capacity label on a typical household bucket: 9 ___.
- What does a kitchen scale measure: length, mass or capacity?
- What does L stand for on a bottle?
- A desk is labelled 120 kg long. Correct the unit and explain.
Read the worked solutions
- Choose cm or m for a pencil length.
A pencil is a short object.
cm - Choose g or kg for the mass of a child.
A child has a mass of many kilograms.
kg - Choose mL or L for the capacity label on a typical household bucket: 9 ___.
9 mL is tiny; a bucket can hold several litres.
L - What does a kitchen scale measure: length, mass or capacity?
Scales measure how heavy something is.
Mass - What does L stand for on a bottle?
L is a capacity unit.
Litre - A desk is labelled 120 kg long. Correct the unit and explain.
Length needs a length unit.
120 cm is a sensible desk length.
120 cm is sensible; kg measures mass.
Curriculum reference & lesson scope
Australian Curriculum v9 and SA Curriculum
Length/mass/capacity units; estimation; reading labelled measuring instruments.
Official curriculum source ↗