Year 2: Centimetres and metres
Part of the Year 2 length, mass, capacity and temperature chapter. Chapter overview · whole chapter on one page
Centimetres and metres
We measure length to find how long something is.
A centimetre is a short unit. We write it as cm. Use cm for a pencil.
A metre is a longer unit. We write it as m. Use m for a door or a bus.
There are 100 cm in 1 m.
Key ideas
- A centimetre (cm) is a short unit. Use it for small things.
- A metre (m) is a longer unit. Use it for big things.
- 1 m = 100 cm.
- Think about the size of the thing before you choose the unit.
Method. Think about the size of the thing before you choose the unit.
- Think about how big it is. A pencil is short. It is only a few centimetres long.a pencil
- Choose the unit that fits. cm is the right size for a pencil.cm
- Write the answer. cm
Check. Would another unit feel right? No. ✓
Watch out. Small things use small units. Big things use big units.
Method. Each m is 100 cm. Multiply.
- Know the rule. 1 m is the same as 100 cm.1 m = 100 cm
- Multiply. Multiply the number of m by 100.2 × 100 = 200
- Write the answer. 200
Check. Share it back: 200 cm is 2 lots of 100 cm. ✓
Watch out. Multiply when you change to a smaller unit. There are 100 cm in 1 m.
Method. Change to the same unit, then pick the biggest amount.
- Look at A. A is 1 m.A: 100 cm
- Look at B. B is 90 cm.B: 90 cm
- Pick the one with the biggest amount. Once the units match, the numbers can be compared.A wins
- Write the answer. A
Check. Compare the other amounts too. ✓
Watch out. Read the units first. 2 m is longer than 150 cm, because 2 m = 200 cm.
Watch out
Watch out: a metre is longer than a centimetre.
Do not measure a bus in cm. Use m.
Exam tip
Grown-up tip. Ask: “Would you use a big or a small unit for this?” Find one thing in the house to measure in cm, and one to measure in m.
Exercise 5A Choosing cm and m
Non-calculatorMethod. Think about the size of the thing before you choose the unit.
- Think about how big it is. A pencil is short.a pencil
- Choose the unit that fits. cm is the right size for a pencil.cm
- Write the answer. cm
Check. Would another unit feel right? No. ✓
Watch out. Small things use small units. Big things use big units.
Method. Think about the size of the thing before you choose the unit.
- Think about how big it is. A door is tall. Its height is more than one metre.a door
- Choose the unit that fits. m is the right size for a door.m
- Write the answer. m
Check. Would another unit feel right? No. ✓
Watch out. Small things use small units. Big things use big units.
Method. Think about the size of the thing before you choose the unit.
- Think about how big it is. A worm is small. Count it in centimetres.a worm
- Choose the unit that fits. cm is the right size for a worm.cm
- Write the answer. cm
Check. Would another unit feel right? No. ✓
Watch out. Small things use small units. Big things use big units.
Method. One metre is the same as two lengths of 50 cm.
- Look at the picture. One metre is one block. Two pieces of 50 cm make the same length.50 + 50
- Add the centimetres. Each piece is 50 cm, so add the two pieces.50 + 50 = 100
- Write the answer. 100
Check. 100 cm is the same as 1 m, so 1 m = 100 cm. ✓
Watch out. There are 100 centimetres in every metre.
Method. Each m is 100 cm. Multiply.
- Know the rule. 1 m is the same as 100 cm.1 m = 100 cm
- Multiply. Multiply the number of m by 100.3 × 100 = 300
- Write the answer. 300
Check. Share it back: 300 cm is 3 lots of 100 cm. ✓
Watch out. Multiply when you change to a smaller unit. There are 100 cm in 1 m.
Method. Each m is 100 cm. Multiply.
- Know the rule. 1 m is the same as 100 cm.1 m = 100 cm
- Multiply. Multiply the number of m by 100.4 × 100 = 400
- Write the answer. 400
Check. Share it back: 400 cm is 4 lots of 100 cm. ✓
Watch out. Multiply when you change to a smaller unit. There are 100 cm in 1 m.
Method. Change to the same unit, then pick the biggest amount.
- Look at A. A is 3 m.A: 300 cm
- Look at B. B is 250 cm.B: 250 cm
- Pick the one with the biggest amount. Once the units match, the numbers can be compared.A wins
- Write the answer. A
Check. Compare the other amounts too. ✓
Watch out. Read the units first. 2 m is longer than 150 cm, because 2 m = 200 cm.
Method. Write 150 cm with a metre and centimetres.
- Look at the length. There is one whole metre inside 150 cm.100 cm = 1 m
- Find what is left. The rest is 150 cm take away 100 cm.150 - 100 = 50
- Write the answer. 1 m 50 cm
Check. 1 m and 50 cm make 150 cm: 100 + 50 = 150. ✓
Watch out. Keep the metres first, then the centimetres.
Method. Compare the rope with the length Ruby needs.
- Look at Ruby’s rope. Her rope is 1 m, which is 100 cm.100 cm
- Look at what she needs. She needs 60 cm.60 cm
- Compare. Is 100 cm more than 60 cm? Yes.100 > 60
- Write the answer. Yes
Check. Her rope is long enough: 100 cm is more than 60 cm. ✓
Watch out. Change to the same unit before you compare.
Method. A pencil is much shorter than a metre.
- Think about a pencil. A pencil is only a few centimetres long.about 15 cm
- Compare with 2 m. 2 m is 200 cm, which is a very long length for a pencil.200 cm
- Decide. Ben is not right.No
Check. A pencil is measured in centimetres, not metres. ✓
Watch out. A pencil is measured in cm. A rope or a door can be in m.
Method. Change 2 m to cm first. Then take away the piece cut off.
- Change 2 m to cm. 1 m = 100 cm, so 2 m = 200 cm.2 × 100 = 200
- Take away the piece. The piece cut off is 50 cm.200 − 50 = 150
- Write the answer. 150
Check. Put the piece back: 150 + 50 = 200. ✓
Watch out. Change to the same unit before you take away.