The volume of a body is a measure of how much space it takes up. The unit in which we measure volume is the litre, or the cubic decimetre. Although volumes are usually measured in litres (l), or millilitres (ml), in fact the litre is not a volume unit of the SI system.

• The SI unit of volume is the cubic decimetre. In other words, it is a cube with all of its sides one tenth of a metre in length ('deci' means one tenth).
•  One litre of volume is the same volume as one cubic decirmetre. We will ordinarily use litres in this book when referring to volumes.

Volume and capacity

The terms 'volume' and 'capacity' have similar meanings, but they are not exactly the same.

The word 'capacity' refers to the amount that can be held in some sort of container. We talk about the capacity of a tea cup, or a swimming pool or of the petrol tank of a car. A doctor may be interested in the capacity of your lungs (how much air your lungs can hold). The unit in which we measure capacity is the same as for volume: the litre.

A capacity is a volume: it is the volume that can be carried in a container.

We could talk about the capacity of a car's boot (luggage compartment) being about 500 litres or the capacity of a refrigerator being about 300 litres.

Scientists use various instruments to measure volumes of liquid. A pipette is a graduated tube. Pipettes are made in different capacities. There are pipettes designed to measure very small actions of a millilitre. The biggest pipettes may measure as much as 100 ml. The word 'pipette' comes from French and means a 'small pipe'.

Bigger volumes are measured in measuring jars, or in volumetric Basks.

We all use graduated items in the home mainly the kitchen. The picture shows some of the things used to contain and deliver known volumes of liquid.