Weekly Hair Extension Tip for February 8,2012 How Many Hair Extensions Do I Need for a Full Head Installation? A full head of extensions range from 5 to 9 packs of hair, assuming each pack contains 20 strands, 1g per strand. If your client has fine, thin hair with some layers and about shoulder length, chances are 5 to 6 packs may be enough. If your client has a blunt bob that is medium to thick in density, you will...