Good question. From my experience as a Personal Trainer and Fitness Director, as well as an independent personal trainer, the number of clients you have will depend on several factors.
One of the first that you will have to take into account is the overall potion of the location you are working at. This can be very different depending upon whether you are working for a health club, private training studio, or independently.
Another important factor is whether you are responsible acquiring clients on your own or if that sales responsibility is up to the membership consultants, fitness managers, or other members of the staff.
From what I have seen Personal Trainers that are new to the industry that have trouble acquiring a clientele in a heavily poted health club will have more trouble supporting their business should they choose to become independent too soon. In addition to a strong technical background, you will have to understand fitness marketing, personal training sales, and networking.
Great luck on your fitness journey,
David I. Bohmiller, BS, NSCA-CSCS
My Personal Trainer School LLC My Personal Trainer School