The Litre

A bottle of water says "1.5 l". A medicine spoon says "5 ml". A car's tank holds "50 litres". None of these is a length or a mass. They tell you how much something holds. What are they measuring?

How much space

How much space something takes up, or how much a container can hold, is called its volume. A bucket has more volume than a cup. A swimming pool has more volume than a bath.

The metric unit of volume used every day is the litre, symbol l (or L, so it doesn't look like the number 1).

A cube of 10 centimetres

Here is how big a litre is. Make a box shaped like a cube (six square sides, like a dice) that is 10 cm long, 10 cm wide and 10 cm tall. Fill it with water. The water inside is one litre.

A cube 10 centimetres long, 10 centimetres wide and 10 centimetres tall holds exactly one litre

In the Kilo, Centi, Milli lesson we saw that milli means a thousandth. So a millilitre (ml) is a thousandth of a litre, and 1 litre = 1,000 ml. A millilitre is a tiny cube, 1 cm on each side. A teaspoon holds about 5 ml.

A litre of water is a kilogram

In the Kilogram lesson we saw that the kilogram was first taken from water. Now you can see how: one litre of water has a mass of about one kilogram. So a millilitre of water is about a gram.

A 1-litre bottle of water on a kitchen scale. The scale shows about 1 kilogram

This only works for water. A litre of cooking oil has a little less mass, about 0.9 kg; a litre of honey has much more, about 1.4 kg. Each one packs a different amount of stuff into the same space.

Try it at home

Put an empty jug on a kitchen scale and set the scale to zero (most have a button for this).
Pour in water until the scale shows 500 g. Look at the jug's markings: is it about 500 ml, half a litre?
Find the volume on three bottles or cartons in your kitchen.

Words to know

volume - how much space something takes up, or how much a container holds
litre (l or L) - the volume of a cube 10 cm on each side
millilitre (ml) - a thousandth of a litre; 1,000 ml = 1 l
cube - a box shape with six equal square sides

Big idea

Volume is how much space something takes up, measured in litres and millilitres. A litre is a cube 10 cm on each side, and a litre of water has a mass of about one kilogram.