The idea, step by step
What are you measuring?
Length tells how far or how long. Mass tells how heavy an object is. Capacity is how much a container can hold. Temperature tells how hot or cold something is. Name the quantity before choosing an instrument.
A ruler measures length, scales measure mass, a measuring jug measures volume of liquid, and a thermometer measures temperature. The number alone is not enough: 25 centimetres and 25 degrees Celsius describe different things.
Choose a useful metric unit
Use millimetres or centimetres for small lengths and metres for larger lengths. Grams suit light objects and kilograms suit heavier ones. Millilitres suit small liquid amounts; litres suit larger amounts. Temperature is commonly read in degrees Celsius, written °C.
Choose a unit that gives a practical number. A pencil might be 18 cm long, not 18 m. A full drink bottle might hold 600 mL, not 600 L. Use a reasonable estimate to check a measurement.
A common trap
The number is the measurement, so I do not need to write a unit.
Instead: A complete measurement needs a number and a unit, such as 24 cm or 24 °C.
See the thinking
Match object, instrument and unit
How would you measure the length of a workbook?
- The quantity is length.
- A ruler is suitable for a straight workbook edge.
- Centimetres give a useful-sized number.
Compare units for capacity
A small medicine cup holds 20 of a metric liquid unit. Is 20 mL or 20 L sensible?
- The cup is small, so litres would describe far too much.
- Millilitres measure small liquid amounts.
- Choose 20 mL; a normal household bucket is much larger than this cup.
Check your understanding
Which is a sensible mass for a school bag: 4 kg or 4 mL?
Show answer
4 kg
Kilograms measure mass; millilitres measure liquid amount or capacity.
Your turn
6 questions · 9 marks · Work at your own pace.
Read the questions online
- Name the quantity measured by a thermometer.1 mark
- Choose a useful unit for a classroom's length: cm, m or °C.1 mark
- Choose a sensible capacity for a drink carton: 250 mL or 250 L.1 mark
- Match ruler, kitchen scales and measuring jug to length, mass and liquid amount.3 marks
- A learner writes that a pencil has a mass of 15 cm. Explain and correct the unit type.2 marks
- A parcel has a mass of 1000 g. Use 1000 g = 1 kg to express its mass in kilograms.1 mark
Read the worked solutions
Equivalent correct methods earn the corresponding marks. Include units where asked.
- Name the quantity measured by a thermometer.1 mark
A thermometer tells how hot or cold something is.
Temperature. - Choose a useful unit for a classroom's length: cm, m or °C.1 mark
It is a length.
Metres give a practical number for a room.
Metres (m). - Choose a sensible capacity for a drink carton: 250 mL or 250 L.1 mark
A small carton cannot hold hundreds of litres.
250 mL. - Match ruler, kitchen scales and measuring jug to length, mass and liquid amount.3 marks
Use the instrument designed for each quantity.
Ruler: length; scales: mass; jug: liquid amount. - A learner writes that a pencil has a mass of 15 cm. Explain and correct the unit type.2 marks
The quantity and unit must match.
A sensible possible pencil mass is 15 g; the actual pencil must be weighed.
Centimetres measure length, not mass. A mass could be stated in grams. - A parcel has a mass of 1000 g. Use 1000 g = 1 kg to express its mass in kilograms.1 mark
The given equality states that 1000 grams is one kilogram.
1 kg
Curriculum reference & lesson scope
Australian Curriculum v9 and SA Curriculum Mathematics 2026
Length/mass/capacity/temperature; scaled instruments; partial/unmarked intervals; suitable units and accuracy.
Official curriculum source ↗