Choosing the Right Unit
Choose appropriate metric units when measuring the length, mass and capacity of objects; use smaller units or a combination of units to obtain a more accurate measure.
Read this first
Pick a unit that gives a sensible number. Small units for small things.
Each unit is bigger than the one before it.
Words you need
- Unit
- What we measure in.
- Convert
- Change from one unit to another.
- Accurate
- Close to the true measure.
Worked example
e.g. Which unit would you use for the length of a pencil?
- Try metres. A pencil is 0.18 m. That is an awkward number.
- Try millimetres. It is 180 mm. That works, but it is long.
- Try centimetres. It is 18 cm. That is the tidiest.
- Use centimetres for a pencil.
A good unit gives a number that is easy to say and picture.
Practice
The pictures fade as you go. By the last few you are on your own.
1Which unit for the height of a door?with a picture
AnswerMetres. About 2 m.
2Which unit for the distance to the next town?with a picture
AnswerKilometres.
3How many centimetres in 3 metres?with a hint
Need a hint?
One metre is 100 cm.
Answer300 cm.
4How many grams in 2 kilograms?with a hint
Need a hint?
One kilogram is 1000 g.
Answer2000 g.
5Which unit for the mass of an apple?on your own
AnswerGrams.
6How many millilitres in 1.5 litres?on your own
Answer1500 mL.
7Why measure a nail in millimetres, not metres?on your own
AnswerMetres would give a tiny decimal that is hard to picture.
Think about it
1
When would you use two units together?
One good answerFor something like 1 m 20 cm, when one unit alone is awkward.
2
Why do smaller units give a more accurate measure?
One good answerYou can measure to a finer mark.
Common mistakes
Using a huge unit for a small thing.
0,002 km is hard to picture. Say 2 m.
Forgetting to convert before adding.
Change both to the same unit first.