Measures in the primary curriculum

Capacity - part 1

The distinction between volume and capacity

The volume of an object is the amount of three-dimensional space that it occupies. By historical accident, liquid volume and solid volume are conventionally measured in different units, although the concepts are exactly the same. Liquid volume is measured in litres and millilitres, and so on, whereas solid volume would have to be measured in units such as cubic metres and cubic centimetres. In the metric system the units for liquid and solid volume are related in a very simple way: 1 millilitre is the same volume as 1 cubic centimetre; or 1 litre is the same volume as 1000 cubic centimetres – get a picture of a one-litre box and a one thousand cubic centimetre cube.

Only containers have capacity. The capacity of a container is the maximum volume of liquid that it can hold. Hence capacity is measured in the same units as liquid volume. For example, if a wine glass holds 180 millilitres of wine when filled to the brim then its capacity is 180 millilitres.

Remember that it is not necessary to do much work on solid volume, measured in cubic centimetres, in the primary age range. But the measurement of liquid volume and capacity, in litres and millilitres, because of the scope for practical experience with water and various containers, is an important component of primary school mathematics.