Here is a bit of fitness info that might be of interest. This is from Michael Scott Scudder on group fitness classes.
First, establish your Maximum Room Capacity:
Square Footage of your exercise room less 100 Divide that number by 35
This number is your maximum number of participants per class

Example: 1500 square foot exercise room (1500 - 100 = 1400/35  = 40 - your  MRC)