### What is length?

When we are comparing and describing length, height, width, breadth, distance, how far or how long, we are using length measurement. Before year 5 you may have used paces or handspans to measure length informally. You may also be familiar with metric units of measurement. The most commonly used units of length measurement are millimetres, centimetres and metres:

- 1 metre = 1000 millimetres.
- 1 metre = 100 centimetres.
- 1 centimetre = 10 millimetres.
- 1 kilometre = 1000 metres.

We sometimes abbreviate the unit of measurement. Metre is shortened to m, centimetre is cm and millimetre is mm.

#### Appropriate choice of unit

If you wanted to measure the length of a piece of ribbon you might use centimetres or metres. You would not use centimetres or metres to measure the distance travelled on an around-the-world holiday. We need to carefully choose units appropriate to the task. This is best learned by doing lots of actual measurement with a range of measuring tools.