We should already be familiar with units used for the measurement of length, area, volume and weight. There are many units for each, but we are only concerned with the related units that can be converted in a straightforward way.
Units of length: millimetres (mm), cenitmetres (cm), metres (m) and kilometres (km).
Units of volume: millilitres (ml) and litres (l).
Units of weight: grams (g) and kilograms (kg).
To convert between related units, multiply or divide by 10, 100 or 1000.
Important: When the unit is smaller, we multiply. When the unit is bigger, we divide.
cm to mm → multiply by 10
mm to cm → divide by 10
m to cm → multiply by 100
cm to m → divide by 100
km to m → multiply by 1000
m to km → divide by 1000
l to ml → multiply by 1000
ml to l → divide by 1000
kg to g → multiply by 1000
g to kg → divide by 1000