In looking for a 'hall' to rent for an event, I was referred to a place that had a 'gym' for rent. When I asked about the gyms size, they replied that it was actually a foot smaller than a regular gym, that it was 99 by 66 feet. I'm not sure if a regular gym would then be 100 by 66 or 99 by 67, but maybe that gets you in the ballpark. This may help improve this answer: The standard dimensions of an NBA basketball court are 50 feet wide by 94 feet long. Obviously additional space is needed at each end and on each side especially if spectator seating is desired. Allowing 8 feet on each side and 3 feet on each end gives 66 feet wide by 100 feet long for a very cozy but usable gym. If your ceiling height is less than 20 feet, you're looking for trouble!