When preparing punch for a party of 100 people, count on each person having four drinks. At eight ozs, this comes to 3200 ozs of punch. That may seem excessive, but you have to account for the duration of the event. If the event lasts two hours or more and food is served, people will drink more often. If you plan on serving other beverages at the function, you can split the number between the other drinks. Not everyone likes punch, so having bottled water, soda, tea, and coffee can reduce the amount of punch you need to make.