Converting metric length
Metric length units go up in steps of 10, 100 and 1 000: 10 mm in 1 cm, 100 cm in 1 m, and 1 000 m in 1 km.
A worked example
Change 3.2 m to centimetres. A centimetre is smaller than a metre, so you need more of them, and you multiply. There are 100 cm in 1 m, so 3.2 × 100 = 320 cm. Change 4 500 m to kilometres. A kilometre is bigger, so you divide: 4 500 ÷ 1 000 = 4.5 km. Recap: to go to a smaller unit, multiply. To go to a bigger unit, divide.
The mistake people actually make
Check that your answer makes sense. 3.2 m is about the height of a room, so 0.032 cm cannot be right. The prefix tells you the size: milli means one thousandth, centi means one hundredth, and kilo means one thousand.