The idea, step by step
A thoughtful guess
An estimate should be based on something familiar. A ruler is often 30 cm long; a litre bottle is a useful capacity benchmark.
You do not need to be exact. The estimate helps you notice when a measured answer seems surprising.
Estimate, measure, compare
First say an estimate and its unit. Next use a suitable tool to measure fairly. Then compare the two values.
If you estimated a book as 25 cm long and measured 27 cm, your estimate was 2 cm short. An estimate of 2 m would be much too long.
A common trap
Using a random number with no reason.
Instead: Choose a benchmark and explain why the size could fit.
See the thinking
A ribbon
A ribbon looks a little longer than a 30 cm ruler. Choose 35 cm or 3 cm as an estimate.
- It must be longer than 30 cm.
- 35 cm is a little longer, while 3 cm is shorter.
A bag
Sam estimates a bag at 2 kg. The scale shows 3 kg. How far apart are the values?
- Both values use kilograms.
- 3 − 2 = 1.
Check your understanding
A bottle holds about 1 L. Is 950 mL or 9 mL closer?
Show answer
950 mL
1 L equals 1,000 mL, and 950 is close to 1,000.
Your turn
6 questions · Work at your own pace.
Read the questions online
- Choose a sensible door height: 2 m or 2 cm.
- Choose a sensible teaspoon capacity: 5 mL or 5 L.
- A bag weighs 4 kg. Was an estimate of 3 kg too high or too low?
- A page measures 29 cm. Which estimate was closer: 30 cm or 20 cm?
- Name a tool to check an estimated table length of 1 m.
- Estimate the capacity of a small drinking cup. Explain your unit.
Read the worked solutions
- Choose a sensible door height: 2 m or 2 cm.
2 cm is a tiny length.
2 m - Choose a sensible teaspoon capacity: 5 mL or 5 L.
Litres suit much larger containers.
5 mL - A bag weighs 4 kg. Was an estimate of 3 kg too high or too low?
4 − 3 = 1 kg.
Too low by 1 kg. - A page measures 29 cm. Which estimate was closer: 30 cm or 20 cm?
30 is 1 cm away; 20 is 9 cm away.
30 cm - Name a tool to check an estimated table length of 1 m.
Use a tool that measures length.
A metre ruler or measuring tape. - Estimate the capacity of a small drinking cup. Explain your unit.
A cup holds part of a litre.
Other sensible cup-sized estimates are acceptable.
Example: about 250 mL.
Curriculum reference & lesson scope
Australian Curriculum v9 and SA Curriculum
Length/mass/capacity units; estimation; reading labelled measuring instruments.
Official curriculum source ↗