Year 3 · Mathematics · Measurement
Measuring with metric units
Measuring and comparing length in centimetres and metres, mass in grams and kilograms, and capacity in millilitres and litres, using rulers, scales and jugs.
Awaiting educator review. This material was drafted by our content team with AI assistance and is waiting for review by a qualified educator. Please check it suits your child before using it. Created 10 October 2026.
Learning goals
Learners will
- Choose a sensible metric unit to measure length, mass or capacity.
- Measure lengths accurately with a ruler in centimetres.
- Know that 1 metre is 100 centimetres, 1 kilogram is 1000 grams and 1 litre is 1000 millilitres.
Success looks like
- I can measure an object with a ruler, starting from zero.
- I can choose centimetres or metres to measure length.
- I can compare masses and capacities using grams, kilograms, millilitres and litres.
- I can solve simple problems with measurements.
The big idea
Informal units like hand spans are different for everyone. Metric units are the same everywhere, so everyone gets the same answer. Australia uses the metric system for everyday measuring.
Length is measured in centimetres (cm) and metres (m). A fingernail is about 1 cm wide; a door is about 1 m wide. There are 100 cm in 1 m.
When using a ruler, line up the end of the object with the 0 mark, not the edge of the ruler. Read the number where the object ends. If the object starts at 2 cm and ends at 9 cm, it is 9 − 2 = 7 cm long.
Mass is how heavy something is. We use grams (g) for light things like a slice of bread and kilograms (kg) for heavier things like a watermelon. 1 kg = 1000 g, so a 1 kg bag of flour is heavier than a 500 g packet of rice.
Capacity is how much a container holds. Millilitres (mL) suit a teaspoon or a cup; litres (L) suit a bucket or a bathtub. 1 L = 1000 mL. Pour water from a 1 L carton into a measuring jug to see this.
- Length: cm, m (100 cm = 1 m)
- Mass: g, kg (1000 g = 1 kg)
- Capacity: mL, L (1000 mL = 1 L)
Worked examples
Measuring with a ruler
A crayon is placed on a ruler. One end is at the 2 cm mark and the other end is at the 9 cm mark. How long is the crayon?
- The crayon does not start at 0, so we cannot just read the end number.
- Find the difference between the marks: 9 − 2.
- 9 − 2 = 7.
Answer: The crayon is 7 cm long.
Comparing masses
Which is heavier: a 1 kg bag of flour or two 400 g packets of pasta?
- Change 1 kg into grams: 1 kg = 1000 g.
- Two packets of 400 g is 400 + 400 = 800 g.
- 1000 g is more than 800 g.
Answer: The 1 kg bag of flour is heavier, by 200 g.
Solving a length problem
A ribbon is 45 cm long. Grace cuts off 20 cm. How much ribbon is left?
- The ribbon gets shorter, so subtract: 45 − 20.
- Take away 2 tens from 4 tens: 4 tens − 2 tens = 2 tens, and the 5 ones stay.
- 45 − 20 = 25.
Answer: 25 cm of ribbon is left.
Practice check
Have a go, then check your answers. Each answer comes with an explanation.
Answer guide for parents
Which unit is best for measuring the length of a pencil?
centimetres — A pencil is short, so centimetres are best. Kilograms measure mass and litres measure capacity.
How many centimetres are in 1 metre?
100 — 1 metre = 100 centimetres.
Which is heavier: 1 kg of flour or 500 g of rice?
1 kg of flour — 1 kg = 1000 g, and 1000 g is more than 500 g, so the flour is heavier.
How many millilitres are in 1 litre?
1000 — 1 litre = 1000 millilitres.
Which of these is most likely to hold about 1 litre?
a small carton of milk — Small milk cartons are often 1 L. A teaspoon and an egg cup hold much less, and a bathtub holds far more.
A piece of string is 60 cm long. Tom cuts off 35 cm. How many centimetres of string are left?
25 — 60 − 35 = 25. Count on from 35 to 60: 5 to get to 40, then 20 more to 60, which is 25.
A leaf is placed on a ruler. One end is at the 3 cm mark and the other end is at the 11 cm mark. How long is the leaf?
8 cm — The leaf does not start at 0, so find the difference: 11 − 3 = 8 cm.
A bag of apples has a mass of 2 kg and a bag of potatoes has a mass of 3 kg. What is their total mass in kilograms?
5 kg — 2 kg + 3 kg = 5 kg.
Watch out for
- Starting a measurement from the edge of the ruler instead of the 0 mark. Show how many rulers have a small gap before 0.
- Thinking bigger objects are always heavier (a pillow versus a tin of beans). Weigh both on kitchen scales to test.
- Confusing mass and capacity units, such as saying a bottle holds 1 kg. Sort food packets into 'g/kg' and 'mL/L' piles.
Tips for parents
- Cooking and baking are perfect measuring lessons: let your child weigh flour and measure milk.
- Check the labels on groceries together and compare grams, kilograms, millilitres and litres.
- Encourage estimating before every measurement and celebrate getting closer over time.
Go further
- Bake a simple recipe together, measuring all the ingredients, and double or halve one ingredient to see what changes.
- Find five things in the house that are about 1 m long and five that are about 10 cm long.
- Fill different containers with water and order them by capacity, checking with a measuring jug.