Primary 2 maths · Measurement & time · About 8 minutes
Measure and compare mass in grams and kilograms
Read the quantity and unit labels before calculating a difference.
Start the interactive lesson →Open practice activity
What you will learn
- Measure and compare mass in grams and kilograms
Models used: number sentences, stories, tables.
Before you start
Compare masses in the same unit
Two packets have masses of 300 g and 500 g. Which is heavier?
Both bars use the same scale. Compare their lengths and read the names beside them.
Read the unit with each number. Both measurements use the same unit, so their numbers can be compared.
Length, mass and liquid volume need suitable units. The scale tells us what each interval or displayed amount represents.
Both bars use the same scale. Compare their lengths and read the names beside them.
500 g is the greater measurement. The longer bar represents the larger amount, not a drawing of the object’s shape.
500 > 300
Both bars use the same scale. Compare their lengths and read the names beside them.
Grams suit light objects; kilograms suit heavier ones. Keep the unit beside the reading.
500 − 300 = 200 g
What did the picture help us see?
Grams suit light objects; kilograms suit heavier ones. Keep the unit beside the reading.
Worked example: A new example, together
One bag measures 7 kg and another 9 kg. What is the difference?
| First reading | Second reading |
|---|---|
| 7 kg | 9 kg |
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 7 kg 9 kg Compare readings in the same unit. Read each value with the heading above its column.
Both measurements use the same unit.
Compare readings in the same unit First reading Second reading 7 kg 9 kg One bag measures 7 kg and another 9 kg. What is the difference?
2 kg
Compare readings in the same unit. Read each value with the heading above its column.
Both measurements use the same unit.
Compare readings in the same unit First reading Second reading 7 kg 9 kg Compare readings in the same unit. Read each value with the heading above its column.
9 − 7 = 2.
Compare readings in the same unit First reading Second reading 7 kg 9 kg Compare readings in the same unit. Read each value with the heading above its column.
The difference is 2 kg.
Compare readings in the same unit First reading Second reading 7 kg 9 kg 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 2 kg. Comparing measurements requires matching the amount and unit.
Compare readings in the same unit First reading Second reading 7 kg 9 kg
Common mistakes to discuss
- Comparing numbers across different units. Change both amounts to the same unit before comparing. 700 g is less than 1 kg, although 700 is the larger number.
Check your understanding
- Measure and compare mass in grams and kilograms
- 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.
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