The capacity of an event is the number of people attending divided by the amount of space needed by each guest. Determining the capacity allows for an event to meet health and safety regulations, and for each guest to be comfortable. If you are planning an event, the capacity will vary depending on whether the guests are standing or sitting. You will also need to work out the exit capacity in case of emergency.

Measure the room where the event will take place and create a scale plan of the space. Measure and include all decorations and furniture that take up space. Make your scale plan as detailed as possible.

Calculate the total area by multiplying the length of the room by its width. Work out the area taken up by furniture and decorations by multiplying the length of the each item by its width. Add up all of the furniture, decorations, and other unusable space. Subtract the unusable space from the total area of the room. What remains is the usable area.

Divide the total area of the room by the amount of space you wish each person to have. For a standing-room-only reception, the Convention Industry Council Manual guidelines recommend 10 square feet per person. Therefore, if your usable space is 1,000 square feet, your capacity is 100 people. This is the maximum number of people who could comfortably fit into the room. If you are hosting a seated banquet, each person will require 13.5 square feet of space, meaning 1,000 square feet will hold 76 people. All other events will be some number in between.

Factor in escape routes for the event. Escape numbers, according to Health and Safety for the Arts, are 73 people per meter of exit for an outdoor event, and 109 people per meter of exit for an indoor event. You need to evacuate the entire event in fewer than 10 minutes, meaning that you use the formula: Exit capacity = Guests / (flow rate x time). At an indoor event with 2,000 guests, the exit capacity must be 2000 / (109 x 10), which means the total door width must be at least 1.83 meters or 6 feet. However, you must factor in that one of the exits may be unusable, so organise for the total door width to be 6 feet when one door is out of action.