An educational resource for primary school students.
Measuring Length
To measure length, we often use:
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millimetres (mm)
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centimetres (cm)
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metres (m)
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kilometres (km)
How big is a millimetre? How big is a centimetre?
A millimetre is VERY small. On your ruler or tape measure, each small line is one millimetre.
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1cm = 10mm​
Every 10 millimetres, you have a centimetre.
This means that 20 millimetres would be 2 centimetres and 60 millimetres would be 6 centimetres. How many centimetres would 90mm be?
Look at the table below to recognise the pattern.
Millimetres and Centimetres
How big is a metre?
1m = 100cm
We use metres to measure longer items such as the distance across a room or the distance from one building in your school to another. The height of buildings is usually measured in metres.
Put a metre ruler against your body. Are you taller than a metre? Do you think you would ever make it to 2m?
Centimetres and Metres
How big is a kilometre?
1km = 1000m
Can you walk a kilometre? Yes, you can.
Depending on where you live, it might be a kilometre to the nearest supermarket.
If your school has cross country, you might to run 2 or 3 kilometres. Longer distances are recorded in kilometres.