It depends on what type of activity you want to do in the space and what type of equipment you are using. Also, take into consideration storage of the equipment (if you are storing it in the studio (eg. mats and weights or balls) that will consume some of your space. Consider “dead space” egress areas, columns etc.
ACSMs Health and Fitness Facility Guidelines (3rd ed.) recommends 40-60 square feet per expected member.
If you are using the space for multiple style classes or activites, I suggest you create studio capacity for each type of activity you offer. This will later serve as a metric to determine whether or not a program or calss is successful.