Follicle Ultrasound. What is enough and what is too much?

This is my 2nd IUI. First one we just used OPKs did the IUI the next day after a positive. I felt that was too much of shot in the dark. So I opted to have an ultrasound (which should have happened in the first place I think) and the HcG trigger shot. I am not taking any meds. Just my prenatals and then the trigger shot. I go in for my U/S today and I was wondering... How many follicles should I have without meds and how many would be too many?? (I am 23 and have no medical problems) Thanks in advance.