Metric Conversions for KS2 SATs

Converting between metric units is one of those topics that sounds simple but catches out loads of children in the SATs. The good news? There are only a handful of conversions your child actually needs to know, and they all follow the same “multiply or divide by 10, 100 or 1000” pattern.

The Key Conversions

Your child needs to know these cold:

Length: 10 mm = 1 cm | 100 cm = 1 m | 1000 m = 1 km

Mass: 1000 g = 1 kg

Capacity: 1000 ml = 1 litre

That’s it. Five conversions. Every measurement question in the SATs uses one of these. If your child can recall them instantly, they’re halfway to the marks already.

Converting to Smaller Units (Multiply)

Going from a bigger unit to a smaller one means you’ll have more of them. So you multiply.

3.5 km → metres

3.5 × 1000 = 3500 m

2.4 kg → grams

2.4 × 1000 = 2400 g

Think of it this way: one kilometre is a long way, so there must be lots of metres in it. More of a smaller unit — multiply.

Converting to Larger Units (Divide)

Going from a smaller unit to a bigger one means you’ll have fewer of them. So you divide.

4500 ml → litres

4500 ÷ 1000 = 4.5 litres

350 cm → metres

350 ÷ 100 = 3.5 m

SATs-Style Word Problems

“A bottle holds 1.5 litres of water. Lucy drinks 350 ml. How much is left? Give your answer in millilitres.”

Step 1: Convert 1.5 litres to ml → 1.5 × 1000 = 1500 ml

Step 2: 1500 − 350 = 1150 ml

Answer: 1150 ml

The key step is converting both amounts to the same unit before calculating. The question tells you which unit to use for your answer — always check.

Common Mistakes to Watch For

Multiplying when they should divide (or vice versa) — ask your child: “Am I going to have more or fewer?” More → multiply. Fewer → divide.
Using the wrong conversion factor — mixing up ×100 with ×1000. Metres to centimetres is ×100, not ×1000.
Forgetting to convert before calculating — you can’t subtract millilitres from litres directly. Same unit first.
Giving the answer in the wrong unit — the question asks for metres but your child gives centimetres. Read the question twice.

Ready to practise?

Build confidence with SATs-style questions

Start Free →