According to About.com, approximately 4 to 4.5 gallons of potato salad are needed to feed 100 people. This assumes a serving size of about 5 ounces per person.
If potato salad is made from scratch to serve 100 people, a basic recipe requires 35 pounds of potatoes, 12 cups of diced celery, 6 cups of diced pickles, 2 cups of minced onions, 1 cup of minced parsley, 18 to 36 hard-boiled eggs and 1.5 to 3 quarts of mayonnaise or other salad dressing. These amounts actually produce about 3.5 gallons of potato salad, which assumes a smaller serving size. Potato salad is traditionally measured in fluid ounces, which means that large amounts are measured in gallons rather than pounds.