Choosing metric units for volume and capacity
21 October 2026
Choosing metric units for volume and capacity
Understanding which metric unit to use for volume and capacity is an important skill for the 11+ maths exam. Children are often asked to match the correct unit to a real-life object or situation.
When to use millilitres and litres
Millilitres (ml) are used for small amounts of liquid, such as a spoonful of medicine or a juice box. Litres (l) are better for larger quantities, such as a bottle of water or a jug of milk.
How to choose the right unit
Think about the size of the object or the amount it holds. If it is something you can drink in one go, like a small bottle, millilitres are likely best. If it is something you would pour out over several uses, litres make more sense.
Worked example
A bottle contains 500 ml of water. Should you use ml or l to describe its capacity?
500 ml is less than 1 litre, so millilitres are the most suitable unit here.
The answer is millilitres.
Key insight: Encourage your child to picture the object in real life. If it fits in a cup or spoon, millilitres are usually right. If it fills a jug or bucket, litres are more suitable.
