Multiply or divide by 10, 100 or 1,000
You learn to convert length, capacity and mass: know how many small units make one big unit, then multiply or divide.
How to work it out
- Know the facts: 1 km = 1,000 m, 1 m = 100 cm, 1 cm = 10 mm, 1 kg = 1,000 g and 1 l = 1,000 ml.
- If you go to a smaller unit, multiply by the fact.
- If you go to a bigger unit, divide by the fact.
A worked example
3 m = ? cm
- 1 m = 100 cm.
- You go to the smaller unit, so multiply by 100: 3 × 100 = 300.
- It is 300 cm.
More examples
2 l = ? ml
- 1 l = 1,000 ml.
- Multiply by 1,000: 2 × 1,000 = 2,000.
- It is 2,000 ml.
2 kg = ? g
- 1 kg = 1,000 g.
- Multiply by 1,000: 2 × 1,000 = 2,000.
- It is 2,000 g.
1,500 m = ? km
- 1 km = 1,000 m.
- You go to the bigger unit, so divide by 1,000: 1,500 ÷ 1,000 = 1.5.
- It is 1.5 km.
Try it yourself
Read the ruler in centimetres
How is the pencil?
From kilometre to metre
2 km = ? m
Watch out
You go the wrong way: 3 m becomes 0.03 cm.
A smaller unit means a bigger number. A cm is small, so there are lots of them in 3 m.
You multiply by 10 every time: 2 kg becomes 20 g.
Check the fact: 1 kg is 1,000 g, so multiply by 1,000. Only cm to mm is 10.
Tips
- Milli is a thousandth, centi is a hundredth and kilo means a thousand.
- Remember three facts: 1 km = 1,000 m, 1 m = 100 cm, 1 cm = 10 mm.
Why it works
A smaller unit fits into a bigger one many times, so you need more of them. A centimetre is small, so there are 100 of them in 1 metre. Kilo means a thousand, and milli means a thousandth.