11+ Maths · Topic explained
Units of measure
Which is longer: 1.5 km or 1400 m?
The big idea
To a smaller unit, multiply. To a bigger unit, divide.
Picture it
Like swapping a £1 coin for 100 pennies: smaller units, more of them.
Key words
- kilo-
- A thousand: 1 kg = 1000 g, 1 km = 1000 m.
- centi-
- A hundredth: 100 cm = 1 m.
- milli-
- A thousandth: 1000 ml = 1 litre, 1000 mm = 1 m.
Worked examples
- 1Warm-up
Change 3 kg into grams.
- 1 kg = 1000 g
- 3 × 1000 = 3000 g
- 211+ standard
Which is longer: 1.5 km or 1400 m?
- Make the units the same: 1.5 × 1000 = 1500 m
- 1500 m > 1400 m, so 1.5 km is longer
- 311+ standard
How many 250 ml glasses can you fill from a 2 litre bottle?
- 2 litres = 2000 ml
- 2000 ÷ 250 = 8 glasses
- 411+ standard
Add 45 mm, 3.2 cm and 0.1 m. Give your answer in cm.
- 45 mm = 4.5 cm, 0.1 m = 10 cm
- 4.5 + 3.2 + 10 = 17.7 cm
The common mistake
The mistake
4.5 kg = 450 g, because you multiply by 100.
Instead
4.5 kg = 4500 g: kilo means 1000.
Why: Each pair of units has its own number: 10, 100 or 1000. Learn which goes with which.
Where it comes up in the 11+
Converting inside word problems: recipes, journeys, drinks and lengths in mixed units.
The video
Video coming soon
We're making a short video that explains units of measure step by step. Until then, everything it covers is on this page.
Free printable
Units of measure worksheet
Practice questions on this topic to print and try on paper, at home or on the way to school.
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Quick quiz
Have a go first, then tap to see the answer.
1. How many millilitres are there in 3.5 litres?
- 350 ml
- 3500 ml
- 35 ml
- 35 000 ml
Show the answerHide the answer
3500 ml
3.5 × 1000 = 3500.
2. What is 750 cm in metres?
- 75 m
- 7.5 m
- 0.75 m
- 75 000 m
Show the answerHide the answer
7.5 m
750 ÷ 100 = 7.5.
3. Which is the heaviest: 1.2 kg, 900 g or 1050 g?
- 1.2 kg
- 900 g
- 1050 g
- They are all the same
Show the answerHide the answer
1.2 kg
1.2 kg = 1200 g, which is more than 1050 g and 900 g.