How many people can attend a party in 3500 square feet?

This is not a math question but rather a question of logistics. The answer depends on how the high the ceiling is , what kind of ventilation the room has , what kind of furniture is in the room and how many exits are in the room. If the room has no furniture like a ballroom and there is good ventilation and enough exits to keep it from being a fire trap, I think 400 people might be able to enjoy a party in such a room.