What space is needed to hold 50 participants in a studio?

Well that depends on how extravagent you wanna be with your lessons. not much space at all is needed if you do an on the spot circuit type session – basically you tell them what the following exercise is going to be and they have all kit needed with them. If you wanna make it more fun and interesting maybe like an hazard circuit. The change is done once the hazard lap is completed how ever many times – do this in pairs one works on the hazards the other on the exercises and you’ll need a space of roughly 15meters x 30meters and some imagination along with a bit of equiptment, (thats just an idea for you 🙂 )
Smudgepti – Brit Army – Infantry – Mil fitness instructor

I’ve comfortably fit 50 into a 1700 sqft area before.

Hi Glora,
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.

I can’t imagine having 50 people in less than 2000 sq. ft. Each person would only have a 6×7 foot area to work in if you are stationary (standard class style). And you aren’t go to be able to mover front to back or side to side much without having people standing still at the edges.