# KS4. Number. Metric units

The metric system, or international system of measurements is used in science and is based on multiples of 10, which makes it easy to use for calculations. You should know the following relationships between metric units:

To convert between units is simply a case of multiplying or dividing by the relevant number. You may have to do this more than once (for instance if you are converting from kilometres to millimetres). In general, if you are converting to a smaller unit you will have to multiply and your answer will be larger, and if you are converting to a larger unit you will have to divide and your answer will be smaller.

Be especially careful with square units or cube units – the conversion numbers can be larger than you think, because, for instance, although a centimetre is only made up of 10 millimetres, a square centimetre is made up of 100 square millimetres. This is easier to see on a drawing.

Exercise

Let’s complete exercises 44 and 45 from pages 121 and 122 of the core textbook: