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.