Converting metric units

Units from the metric system can be used to describe the mass, volume or length of an object.

Mass is measured in grams (g) and kilograms (kg).

Volume is measured in millilitres (ml) and litres (l).

Length is measured in millimetres (mm), centimetres (cm), metres (m) and kilometres (km).

To convert metric units, you need to remember these facts:

Test out your knowledge of converting metric units with this quiz, then read on to complete the page.

Grams and kilograms are metric units which are used when measuring the mass of objects.

Grams are usually used for lightweight objects, while kilograms are used for heavier objects.

The word ‘kilo’ means 'one thousand'. One kilogram is a thousand grams.

1kg = 1,000g

Here are some objects that are weighed in grams and kilograms.

A double number line is a useful tool to use when you want to convert between grams and kilograms.

For example on the number line you can see that:

5kg = 5,000g

To convert from grams to kilograms, you divide by 1,000.

To convert from kilograms to grams, you do the opposite - you multiply by 1,000.

You may also find a bar model helpful when converting grams and kilograms.

This bar model shows how many kilograms or grams are equivalent to 5 kilograms.

Converting millilitres and litres

Millilitres and litres are metric units which are used when measuring volume.

‘Milli’ means ‘one thousandth’. So, a thousand millilitres is 1 litre.

1,000ml = 1 litre

Take a look at these objects and the volume of liquid they might hold.

A double number line is useful when you want to convert millilitres and litres.

To convert from millilitres to litres, you divide by 1,000.

To convert from litres to millilitres, you do the opposite, you multiply by 1,000.

You may also find a bar model useful when converting millilitres and litres.

This bar model shows how many litres or millilitres are equivalent to 5 litres.

Converting millimetres, centimetres, metres and kilometres

When converting millimetres, centimetres, metres and kilometres you need to remember:

10mm = 1cm

100cm = 1m

1,000m = 1km

You will also need to use your knowledge of decimal places when converting measurements of length.

To convert millimetres and centimetres you divide by 100.

To convert centimetres to millimetres you multiply by 1000.

Take a look at the line being measured by this ruler.

To convert from centimetres to metres, you divide by 100.

To convert from metres to centimetres, you multiply by 100.

To convert metres to kilometres you divide by 1000.

To convert kilometre to metres you multiply by 1000.

You may also find a bar model useful when converting metres, centimetres and millimetres.

This bar model shows how many millimetres, centimetres, metres are equivalent to 5 kilometres.