Which unit fits best?
You learn to estimate which unit fits: mm, dm, m, km, g, kg, ml, dl or l.
How to work it out
- Think of something you know: a bag of sugar is 1 kg.
- Compare: much smaller, about the same, or much larger.
A worked example
The height of a door is about 2 …
- Think of a metre: it comes up to about your waist.
- A door is twice as high.
- It is 2 metres.
More examples
The weight of a bag of apples is about 2 …
- Think of a bag of sugar: it weighs a kilogram.
- A bag of apples weighs as much as two bags.
- It is 2 kilograms.
The volume of a teaspoon is about 5 …
- Think of a carton of milk: that is a litre, far too much.
- A teaspoon holds only a few drops.
- It is 5 millilitres.
Try it yourself
Which unit belongs here?
The thickness of a pencil is approximately 3 …
Which unit belongs here?
The volume of a glass of juice is approximately 2 …
Watch out
You choose the first unit you think of: a door 2 kilometres high.
Say the sentence out loud with your unit in it. If it sounds strange, choose a smaller or bigger unit.
You mix up length, mass and capacity: a carton of milk 1 kilogram long.
First look at what you are measuring: how long, how heavy or how much fits in. Then choose a unit of that kind.
Tips
- A millimetre is about as thick as a coin, and a gram is about as heavy as a paperclip.
Why it works
A unit only means something when you can see or feel it. A millimetre is about as thick as a coin, a metre comes up to your waist, a kilogram is a bag of sugar and a litre is a carton of milk. With examples like these you can compare anything.