You should know about the following common metric units of measurement:
Length and Distance
1 km = 1,000 m
1 m = 100 cm = 1,000 mm
1 cm = 10 mm
1 kg = 1,000 g
1 litre = 1,000 ml
These are really important conversions to know, so spend a bit of time learning them.
If you still find it hard to remember, you can look back to this introduction by clicking on the red button at the side of the screen.