Measurement units and precision | Year 5

01 / LEARN

The idea, step by step

Choose a useful unit

Metric units measure different attributes. Use millimetres, centimetres, metres or kilometres for length; grams or kilograms for mass; millilitres or litres for capacity. Decide what you are measuring before choosing a unit.

For a desk, centimetres are more useful than kilometres. For the road between towns, kilometres are more useful than millimetres. Changing units changes the number, not the physical size of the object.

Count intervals and match the scale

Find the difference between two scale labels and count the equal gaps. Divide to find the size of each gap. Count spaces, not tick marks. Start a ruler at zero, or subtract the starting reading from the ending reading.

A measurement depends on the instrument. An endpoint between marks may need an estimate. Do not add decimal places that the scale cannot support. A half-centimetre ruler can show an endpoint exactly on 3.5 cm, but it cannot prove a reading to a thousandth of a centimetre.

A common trap

Count the tick marks instead of the spaces when finding the step size.

Instead: Intervals are the equal gaps between marks. Two end ticks with three ticks between them make four gaps.

02 / WORKED EXAMPLES

See the thinking

Example 1

Read the half-centimetre ruler

Find the object length in the diagram.

Labels are 1 cm apart.
Each centimetre contains two equal gaps, so one gap is 0.5 cm.
The object begins at zero and ends halfway between 3 and 4.

3.5 cm

Example 2

Find the gap size

A jug is labelled 200 mL and 400 mL, with 4 equal gaps between the labels. What does each gap represent?

Difference: $400 - 200 = 200$ mL.
There are 4 gaps.
$200 \div 4 = 50$ mL per gap.
Two gaps above 200 mL would show 300 mL.

50 mL

Check your understanding

A scale goes from 10 kg to 20 kg in 5 equal gaps. What is one gap worth?

Show answer

2 kg

The difference is 10 kg. Divide by the five gaps: $10 \div 5 = 2$ kg.

03 / WORKSHEET

Your turn

6 questions · 11 marks · Work at your own pace.

Worksheet PDF Worked solutions

Read the questions online

Choose a useful metric unit for the distance between towns.
1 mark
Choose a useful metric unit for the mass of an apple.
1 mark
Convert 3 m to centimetres.
2 marks
A jug has 5 equal gaps from 0 mL to 500 mL. Find the size of one gap.
2 marks
A pencil begins at 2 cm and ends at 14 cm on a ruler. Find its length.
2 marks
A ruler has marks every 1 cm. Lee reports an exact length of 7.438 cm after only reading that ruler. Explain the problem.
3 marks

Read the worked solutions

Equivalent correct methods earn the corresponding marks. Include units where asked.

Choose a useful metric unit for the distance between towns.
1 mark
A distance between towns is large enough that kilometres give a useful number.
Kilometres (km)
Choose a useful metric unit for the mass of an apple.
1 mark
Grams give a useful number for an object much lighter than a kilogram.
Grams (g)
Convert 3 m to centimetres.
2 marks
Each metre is 100 cm.
$3 \times 100 = 300$ .
300 cm
A jug has 5 equal gaps from 0 mL to 500 mL. Find the size of one gap.
2 marks
$500 \div 5 = 100$ .
100 mL
A pencil begins at 2 cm and ends at 14 cm on a ruler. Find its length.
2 marks
Subtract the starting reading: $14 - 2 = 12$ cm.
12 cm
A ruler has marks every 1 cm. Lee reports an exact length of 7.438 cm after only reading that ruler. Explain the problem.
3 marks
Its marks show whole centimetres.
Extra decimal digits do not make the measurement more accurate.
The ruler does not show thousandths of a centimetre, so it cannot support that exact reading.

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Curriculum reference & lesson scope

Australian Curriculum v9 and SA Curriculum Mathematics 2026

Units/precision; regular/irregular regions; boundary and area problems.

Official curriculum source ↗

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