Depends whether you are having them dried or fresh, depends on your state of mind and depends on the mood of the mushroom.
I grew and dried cubensis, one time I had a mega giggly trip from only THREE mushrooms, a full on trip from 8 mushrooms and quite a mild trip from about 13 mushrooms. Point being, regardless of the dosage you decide on, things could turn out very unpredictable anyway. If you are going on the actual number of mushrooms to ingest then just start at a couple, you will soon get a feel of where the trip is going and where you want to go and can take more if desired.