When cooking for a group of 100 people, 6.25 gallons of soup are needed when serving as a first course. The suggested serving size per person is 1 cup.
If soup is to be served as the main meal, the amount needed increases. Two cups of soup per person are needed when served as the entree. For 100 people, it would require 12.5 gallons of soup, or 200 cups.
When serving large crowds, it is recommended to always make a little more than needed to ensure everyone is served. If serving appetizers before the meal, cooks should plan on 6 to 8 pieces per person, or a total of 600 to 800 appetizers.