Practical measurement | Year 6

01 / LEARN

Understand the idea.

Choose the unit and method

Choose a unit and tool suited to the object and the detail needed. Millimetres suit a small thickness, centimetres suit a book, metres suit a room and kilometres suit a journey. An estimate helps you notice an unsuitable unit.

A ruler measures the distance between two readings. Line the object up with zero when possible; otherwise subtract its starting reading from its ending reading. For a curved edge, follow it with string or a flexible tape rather than measuring straight across.

Use measurements to make a decision

A practical question often needs measurements combined. To cover a rectangular board with square cards, first find how many fit along each side. Multiplying those counts gives the number of cards when the rows fit exactly.

An area calculation can check a covering problem, but area alone does not always prove that tiles fit. Check the side lengths and the stated conditions, such as no gaps, overlaps or cutting. Keep units consistent throughout the decision.

02 / WORKED EXAMPLES

See the method in action.

EXAMPLE 01

Worked example 1

A ribbon begins at the 2.5 cm mark on a ruler and ends at 14.5 cm. Find its length.

Worked solution

1
Identify the two ruler readings.
$start = 2.5 cm, end = 14.5 cm$
The ribbon begins partway along the ruler rather than at zero.
2
Find the distance between the readings.
$length = 14.5 - 2.5 = 12 cm$
Subtracting removes the unused part of the ruler before the ribbon.
3
Check the ending position.
$2.5 + 12 = 14.5$
Adding the measured length to the starting mark reaches the given ending mark.

Answer

12 cm.

EXAMPLE 02

Worked example 2

A rectangular display board measures 120 cm by 80 cm. It is covered exactly by 20 cm by 20 cm square cards, without gaps or overlaps. How many cards are needed?

Worked solution

1
Count the cards along the length.
$120 \div 20 = 6$
Each card uses 20 centimetres of the 120-centimetre side.
2
Count the rows across the width.
$80 \div 20 = 4$
Four whole card widths fit exactly, so no cutting or gaps are needed.
3
Multiply cards per row by the number of rows.
$6 \times 4 = 24 cards$
Every row contains six cards and there are four rows.
4
Check using areas.
$\begin{aligned} A_{board} & = 120 \times 80 = 9600 {cm}^{2} \\ A_{card} & = 20 \times 20 = 400 {cm}^{2} \\ 9600 \div 400 & = 24 \end{aligned}$
The same total area is covered by the 24 cards already shown to fit along both sides.

Answer

24 cards.

03 / YOUR TURN

Try it yourself.

Check your understanding

An object begins at 3 cm and ends at 11 cm on a ruler. How long is it?

Show answer & reasoning

8 cm.

The object covers the distance from the $3 cm$ mark to the $11 cm$ mark, so its length is $11 - 3 = 8 cm$ .

Keep practising

6 worksheet questions · 9 marks

Open worksheet Worked solutions

Read the questions online

Choose the most suitable unit for a school oval’s length: millimetres, metres or kilometres.
1 mark
A pencil begins at 1.5 cm and ends at 16 cm. Find its length.
1 mark
A rectangular mat is 3 m by 2 m. Find its area.
1 mark
A 2-metre ribbon is cut into eight equal pieces. Find each length in centimetres.
2 marks
A board is 100 cm by 60 cm. Square stickers have sides of 10 cm and cover it without gaps. How many stickers fit?
2 marks
A room width is recorded as 420 m. Suggest a likely unit correction and explain why it is plausible.
2 marks

Read the worked solutions

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

Choose the most suitable unit for a school oval’s length: millimetres, metres or kilometres.
1 mark
The length is large enough for metres but much less than a kilometre.
Metres.
A pencil begins at 1.5 cm and ends at 16 cm. Find its length.
1 mark
$16 - 1.5 = 14.5$ .
14.5 cm.
A rectangular mat is 3 m by 2 m. Find its area.
1 mark
$3 \times 2 = 6$ .
6 square metres.
A 2-metre ribbon is cut into eight equal pieces. Find each length in centimetres.
2 marks
$2 m = 200 cm$ ; $200 \div 8 = 25$ .
25 cm.
A board is 100 cm by 60 cm. Square stickers have sides of 10 cm and cover it without gaps. How many stickers fit?
2 marks
$100 \div 10 = 10$ across and $60 \div 10 = 6$ down; $10 \times 6 = 60$ .
60 stickers.
A room width is recorded as 420 m. Suggest a likely unit correction and explain why it is plausible.
2 marks
A normal room is a few metres wide, not hundreds of metres. The actual unit must be checked rather than silently changed.
420 cm, or 4.2 m, is plausible.

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Curriculum reference & lesson scope

Australian Curriculum v9 and SA Curriculum Mathematics

Decimal metric conversions; deriving rectangle area; missing dimensions; practical measurement.

Official curriculum source ↗

In this lesson

Understand the idea.

Choose the unit and method

Use measurements to make a decision

See the method in action.

Worked example 1

Identify the two ruler readings.

Find the distance between the readings.

Check the ending position.

Worked example 2

Count the cards along the length.

Count the rows across the width.

Multiply cards per row by the number of rows.

Check using areas.

Try it yourself.

Check your understanding

Keep practising