This question is asked all the time and the answer really never changes...
1. Strain is very very relevant to this question as there are strains that will put off heavy yields and some that no matter what you will get get 2.5 zips a plant.
2. Medium... soil, aero, flood & drain, dwc... what is being used to grow.
3. What type of bulb? Yes this is important, straight up tests I have seen a couple certain bulbs add 20-30% to yields.
4. Nute line... what are you using? Are you keeping PH & PPMs in check?
There are literally dozens of things that can effect yield, figure in a 4x4 tent with mid yielding plants and having 7 in there... 2.5-8 zips per plant, all dependent on information I stated above.