Measuring Length, Mass and Capacity: Year 3 Study Guide
Measurement tells us how long, how heavy or how much a container can hold. Australia uses the metric system.
Everything we measure needs a unit. Length is measured in millimetres (mm), centimetres (cm), metres (m) and kilometres (km). Mass, how heavy something is, is measured in grams (g) and kilograms (kg). Capacity, how much a container holds, is measured in millilitres (mL) and litres (L).
Choosing a sensible unit is part of measuring well. You would measure a pencil in centimetres, a swimming pool in metres, a bag of flour in grams or kilograms, and a cup of water in millilitres.
Useful conversions
The metric system uses tens, hundreds and thousands, so conversions are easy to remember.
| Measure | Conversion |
|---|---|
| Length | 10 mm = 1 cm; 100 cm = 1 m; 1 000 m = 1 km |
| Mass | 1 000 g = 1 kg |
| Capacity | 1 000 mL = 1 L |
Reading scales
On a ruler, line up the zero with the end of the object and read where the other end falls. If it lands between marks, record to the nearest centimetre or millimetre. On a measuring jug, read at eye level at the bottom of the curve of the liquid. On kitchen scales, work out what each small mark is worth before reading the pointer.
Check the object begins at 0, not at the end of the ruler.
Say 'about 12 cm' or '12 cm 3 mm'.
A number without a unit is incomplete.
Comparing and estimating
Estimating builds number sense. A standard paperclip is about 3 cm long, a litre of milk has a mass of about 1 kg, and a teaspoon holds about 5 mL. Use these benchmarks to estimate before you measure and see how close you were.
Worked examples and common mistakes
Example: A rope is 2 m 40 cm long. How many centimetres? 2 m = 200 cm, so 240 cm. Example: A recipe needs 750 mL of milk and 250 mL of cream. Together: 1 000 mL, which is 1 L. A common mistake is to read a ruler from 1 instead of 0, giving an answer that is 1 too large. Another is to mix units in a calculation without converting first.
Check your understanding: model answers
1. An apple: grams. A playground: metres. A bucket: litres. 2. 3 L = 3 000 mL. 3. 150 cm = 1 m 50 cm, or 1.5 m.
✨ Key Takeaways
- Choose a unit that fits the size of what you are measuring.
- 1 m = 100 cm, 1 kg = 1 000 g and 1 L = 1 000 mL.
- Always start measuring from zero.
- Estimate first, then measure to check.
💬 Questions for Discussion & Reflection
- Which unit would you use for the mass of an apple, the length of a playground and the capacity of a bucket?
- How many millilitres are in 3 L?
- A ribbon is 150 cm long. How many metres and centimetres is that?
Print a measurement record sheet →