Skill: Choose centimetres or metres

To choose a unit, think about the size of the object or distance:

• Use centimetres (cm) for small objects, such as a pencil or a book.
• Use metres (m) for larger objects or distances, such as a door or a classroom.

Remember:

$$1\text{ metre}=100\text{ centimetres}$$

Example: A classroom door is about 2 units tall. Should we use centimetres or metres?

1. A door is a large object.
2. Large objects are best measured in metres.
3. So, we would say the door is about 2 metres tall.

The length stays the same if we use a different unit. Since $1$ metre equals $100$ centimetres, $2$ metres equals $200$ centimetres. Metres are the better choice because the door is large.