If your hair is very fine and flat on top you should probably go for a 120g set, as the clips will lie flat against your head and will be easy to hide. We also recommend 120g if your hair is already very long and you just want the hair extensions for additional thickness.
If your hair is medium thick and just below your shoulders or shorter and you want to achieve additional length and volume we recommend 160grams.
For very thick hair that is medium length or short we recommend 220grams. This is also what most celebrities use for their extra length and volume.