Choose suitable measurement units

What you will learn

• Choose suitable measurement units

Models used: number sentences, stories, tables.

Before you start

• Measure and compare liquid volume in litres

Choose a unit that fits what you measure

Would you measure the length of a pencil in centimetres, kilograms or litres?

1. First decide what you are measuring. A pencil’s length is a distance, so use a length unit.

   Length → centimetres or metres

   Length, mass and liquid volume need suitable units. The scale tells us what each interval or displayed amount represents.

2. Choose a mass unit. Read each value with the heading above its column.

   Mass tells us how heavy something is. Use grams for a light object and kilograms for a heavier one.

   Choose a mass unit

   What we measure	Suitable unit
   Mass of an apple	grams
   Mass of a child	kilograms

3. Match the kind of measurement first. Read each value with the heading above its column.

   Liquid volume tells us how much liquid a container holds. Litres suit a bottle or jug.

   Match the kind of measurement first

   What we measure	Suitable unit
   Liquid in a jug	litres
   Length of a classroom	metres
   Length of a pencil	centimetres

4. Our pencil question asks for length, so centimetres fit. Kilograms measure mass and litres measure liquid volume.

   Pencil length: 12 cm

Worked example: A new example, together

Choose a suitable unit for the liquid in a bucket.

1. Compare readings in the same unit. Read each value with the heading above its column.

   Read the quantity and unit labels before calculating a difference.

   Comparing measurements requires matching the amount and unit.

   Compare readings in the same unit

   First reading	Second reading
   3 m	11 m

2. Compare readings in the same unit. Read each value with the heading above its column.

   Identify the kind of quantity.

   Compare readings in the same unit

   First reading	Second reading
   3 m	11 m

   Choose a suitable unit for the liquid in a bucket.

   litres

3. Compare readings in the same unit. Read each value with the heading above its column.

   Identify the kind of amount.

   Compare readings in the same unit

   First reading	Second reading
   3 m	11 m

4. Compare readings in the same unit. Read each value with the heading above its column.

   The liquid in a bucket is suitably measured in litres.

   Compare readings in the same unit

   First reading	Second reading
   3 m	11 m

5. Compare readings in the same unit. Read each value with the heading above its column.

   Units must match the amount, not just the size of the number.

   Compare readings in the same unit

   First reading	Second reading
   3 m	11 m

6. Compare readings in the same unit. Read each value with the heading above its column.

   Check the result against the question we started with.

   Re-read the labels and unit before comparing the numbers.

   We found litres. Comparing measurements requires matching the amount and unit.

   Compare readings in the same unit

   First reading	Second reading
   3 m	11 m

Common mistakes to discuss

• Choosing by the size of the number. Choose the unit by the size of the object. A pencil is about 12 cm; 12 m would be longer than a classroom.

Check your understanding

• Choose suitable measurement units
• choose and interpret units that match the measured quantity
• check the answer against the original quantities and units

Explain your reasoning to an adult, then try a fresh question in the interactive lesson. A result from one attempt is not proof of lasting mastery.