11+ Maths: Choosing Metric Units
21 October 2026
Why metric units matter
Choosing the right metric unit is an important skill for 11+ maths. It helps children measure and describe objects accurately, and avoid mistakes in calculations.
Types of metric units
For length, use millimetres (mm), centimetres (cm) or metres (m). For mass, use grams (g) or kilograms (kg). For capacity, use millilitres (ml) or litres (l). The choice depends on the size or amount you are measuring.
When to use which unit
Use millimetres for very small items, like the thickness of a coin. Centimetres are good for everyday objects, such as a pencil. Metres work for larger distances, like the length of a room. For mass, use grams for light objects and kilograms for heavier ones. For capacity, use millilitres for small amounts of liquid and litres for larger amounts.
Tips for recognising the right unit
If a number seems very large or very small, check if a different unit is more suitable. Remember, sometimes you need to convert units to make calculations easier or to answer the question in the required form.
Worked example
A bottle contains 2 litres of water. How many millilitres is that?
Step 1: Know that 1 litre = 1,000 millilitres.
Step 2: Multiply 2 by 1,000.
2 × 1,000 = 2,000
The correct answer is 2,000 millilitres.
Key insight: Choosing the correct metric unit helps children understand the scale of a problem and communicate answers clearly. It also reduces the risk of calculation errors in 11+ exams.
