When you know how many people you plan to invite to your event and the details, such as what type of seating to provide and what elements such as a stage or dance floor you want, you can calculate what size room you need. The numbers vary based on the type of event; a sit-down dinner usually requires more square footage than a stand-up cocktail event. Adding on extras including a stage or buffet table increases the necessary room size.

Changing the seating changes the room size requirements. For round tables of eight or 10 people, figure 10 to 14 square feet per person. If you're using rectangular banquet tables or planning a cocktail-style event, use 8 square feet per person. Dance floors often require 2 to 4 square feet per person. Calculate the stage requirements as the size of the stage plus 25 percent. Groups tend to gather around bars and buffet tables, so allow 100 square feet per 6-foot bar and 60 square feet per 8-foot buffet table.

To determine the necessary room size, add the extras first. If the stage needs 375 square feet, the dance floor needs 200 square feet, and a bar and two buffet tables require 220 square feet, you'll need 795 square feet. Adding in 100 people sitting at rectangular tables increases that number 800 square feet, giving you a total of 1,595 square feet. That's equivalent to a room of about 40 feet by 40 feet.