I am assuming you are referring to members at a gym/fitness center that has classes, private/group training, and unsupervised exercisers.
This actually depends on many things. But one of the biggest influences on the number of class participants is determined by the instructors. Word gets around pretty quickly if an instructor is really fun and energizing.
Another is the popularity of the classes offered.
I have worked at facilities where classes made up close to 80% of the volume. And others where the classes were only 50% or less of the volume.
this is difficult to answer. Most members will participate in at least one class format periodically, and some members don’t do anything else but taking classes.
It may be easier to break it down by gender. I am sure no more that 5 % of male members take classes whereas the number for women is more like 80 %, if not higher.
That’s a really broad question. I think it will depend on:
The size of the city
The number of members of that gym
The number of classes on the schedule
The time of day
How long that instructor has been teaching that class in that time slot.
I get 45-60 for one of my classes, which are great numbers for that club. But I used to teach the same format at a similar time at a club 4 miles away. That’s a large big-box gym with many more members, and 60 was a small class for me.