When we measure, we need the right unit. We measure how long things are, how heavy they are, and how much liquid they hold.
Why this matters: Cooking, shopping and building all need careful measuring. Using the right unit means your cake rises and your shelf fits the wall!
The main units
| We measure | Small unit | Bigger units |
|---|---|---|
| Length | millimetre (mm) | centimetre (cm), metre (m), kilometre (km) |
| Mass (weight) | gram (g) | kilogram (kg) |
| Capacity (liquid) | millilitre (ml) | litre (l) |
Simple conversions
These facts help you swap between units:
- 10 mm = 1 cm
- 100 cm = 1 m
- 1000 m = 1 km
- 1000 g = 1 kg
- 1000 ml = 1 litre
To change 200 cm into metres: 100 cm = 1 m, so 200 cm = 2 m.
Put these length units in order, smallest first:
- mm
- cm
- m
- km
Reading a ruler
On a ruler, each big number is a centimetre. The small lines between them are millimetres. To measure, line up one end of the object with 0, then read where the other end stops.
Choosing the right unit: Use mm or cm for a pencil, m for a room, and km for a car journey. Use g for an apple and kg for a bag of flour. Use ml for a spoon of medicine and litres for a bottle of water.