Choosing metric units for length and mass
21 October 2026
Choosing metric units made simple
Choosing the correct metric unit is an essential skill for 11+ maths. Children need to know when to use millimetres, centimetres, metres or kilometres for length, and milligrams, grams or kilograms for mass. Picking the right unit makes solving problems easier and helps avoid mistakes.
When to use each unit
Millimetres are best for very small objects, like the thickness of a coin. Centimetres are useful for things like pencils or books. Metres work well for furniture or rooms, while kilometres are used for distances between places. For mass, milligrams are for tiny amounts, grams for small objects, and kilograms for heavier items like bags of sugar.
Worked example
A pencil is 15 cm long.
A table is 1.2 m long.
Step 1: Note the length of the pencil as 15 cm.
Step 2: Convert the table's length from metres to centimetres: 1.2 m × 100 = 120 cm.
Step 3: Compare the lengths: 120 cm is longer than 15 cm.
The correct answer is that the table is longer than the pencil.
Tips for choosing metric units
Always check the size of the object before picking a unit. If you need to compare or add measurements, convert them to the same unit first. Practising these choices builds your child's confidence and helps them work accurately in the 11+ exam.
Key insight: Correctly choosing and converting metric units is a practical skill that helps children solve maths problems effectively and succeed in the 11+ exams.
