There’s no absolute formula to calculate how much food and drink is needed for a party, but it’s safe to follow the “one pound rule.” It means that you need to prepare one pound of food for each adult attending your party, excluding drinks and dessert.   For example, if you’re planning to invite 20 adult guests, then you have to prepare no less than 20 pound of food and another 20 pound for drinks. There’s a huge chance that there will be no leftover food with this rule considering that most adults have a huge appetite.