Length
Maths: Year 3 & 4 National Curriculum, topic 2.1.1
Length
Length means the measurement of how long something is or the distance between two places. Metres, centimetres, millimetres and kilometres are all units of length.
Units of length
- In measurement, we use the word unit to describe what measurement we are using.
- Metre, centimetre, millimetre and kilometre are all units of length.
- We write units after the number, using lower case letters.
- 5 m (five metres).
- 20 cm (twenty centimetres).
- 340 mm (three-hundred and forty millimetres).
- 10 km (ten kilometres).
Relations between units
- If you look at your ruler, you will see it shows some units of length.
- Most rulers show centimetres (cm) and millimetres (mm).
- You can see that millimetres are smaller and centimetres are bigger.
- There are 10 millimetres in 1 centimetre.
- There are 100 centimetres in 1 metre.
Mixed units
- Sometimes an object won't have an exact measurement in one unit.
- For example, a car is measured to be 4 and a half metres long.
- That means the length of the car is the same as 4 metres plus 50 centimetres, which is half a metre.
- We write this as 4 m 50 cm or 4 1/2 m.
Measuring objects
- You should use millimetres (mm) to measure small objects like the tip of a pencil.
- You should use centimetres (cm) to measure medium-sized objects like books.
- You should use metres to measure large objects like cars and classrooms.
- You should use kilometres to measure very large distances, for example between towns and cities.
Test yourself on Length
Which unit of length should you use to measure a classroom?
Which unit of length should you use to measure a grain of rice?
Which unit of length should you use to measure the length of a shoe?