Length, Mass and Capacity

Three things we measure

Almost everything we measure in everyday life is one of three things. Each one has a small unit for little things and a large unit for big things — and the trick is to choose the unit that fits.

Length — how long something is. We measure it in millimetres (mm), centimetres (cm), metres (m) and kilometres (km). A pencil is best in centimetres, a person's height in metres, and the distance along a road in kilometres.
Mass — how heavy something is. We measure it in grams (g) and kilograms (kg). An apple is a few hundred grams; a bag of potatoes is a few kilograms.
Capacity — how much a container holds. We measure it in millilitres (ml) and litres (l). A spoonful is a few millilitres; a bottle of water is about one litre.

Always pick the unit that suits the size of the thing — you would not measure a road in millimetres, and you would not weigh a feather in kilograms!

The units, and how they fit together

Each large unit is built out of many small ones. Learn these and you can swap between them.

We measure three everyday things, each with a small and a large unit — pick the one that suits the size of the thing:

Length: millimetres, centimetres, metres, kilometres, with 1 \text{ cm} = 10 \text{ mm}, 1 \text{ m} = 100 \text{ cm} and 1 \text{ km} = 1000 \text{ m}.
Mass: grams and kilograms, with 1 \text{ kg} = 1000 \text{ g}.
Capacity: millilitres and litres, with 1 \text{ l} = 1000 \text{ ml}.

Reading a ruler

Step through the figure: first a centimetre ruler numbered from 0 to 10, then an object resting on it. Start the object at 0 and read off where it ends.