If it's a hearty soup that is served as the meal itself, and served with bread or crackers and salad, then you can figure about 2 cups per person. Since there are 16 cups to a gallon, that would give you 8 servings. If it's a lighter soup that is served as part of a 5 - 7 course meal, then you can figure about 1 cup person, which would be 16 servings.
