L1 · Millimetres, centimetres, metres: relating the units; choosing the right unit

Learning goal

“I can say how millimetres, centimetres, and metres fit together - 10 mm in 1 cm, 100 cm in 1 m - and I can choose the best unit for the thing I am measuring.”

Metre (m) — the basic unit of length. A metre is a big unit, used for long lengths.

Centimetre (cm) — a smaller unit of length. There are 100 centimetres in 1 metre.

Millimetre (mm) — a tiny unit of length. There are 10 millimetres in 1 centimetre.

Length — how long something is from one end to the other. We measure length in units.

Worked example

The three units fit together like this: 10 mm = 1 cm and 100 cm = 1 m. Problem 1: How long is 3 m in centimetres? Step 1: Each metre holds 100 centimetres. Step 2: 3 metres hold 3 x 100 = 300 cm. Problem 2: A mark is at 40 mm. How many centimetres is that? Step 1: Every 10 millimetres make 1 centimetre. Step 2: 40 mm is 4 groups of 10 mm, so 40 mm = 4 cm. Say it plainly: big unit to small unit - the number grows. Small unit to big unit - the number shrinks.

Check yourself — explain it

There are 100 centimetres in 1 metre because...

Paired problem — example still visible

How many millimetres are in 6 cm? -> 60 mm (6 x 10)

Faded completion — last step is yours

"2 m = 2 x 100 = ___ cm" -> 200

Ready to practise?

10 scored questions with a 3-rung hint ladder. Mastery needs 8/10 plus both gate questions.

Start practice →Take the unit quiz