I would make 3.5 pounds
25 pounds should be plenty.
Since 25 pounds feeds 100, you'll need 106 1/4 pounds of potato salad.
A standard serving of mashed potatoe's is around six ounces. Between five and six pounds should be enough to serve 10 adults and maybe even leave you a little bit of leftovers.
7 pounds
If you are making mashed potatoes from raw potatoes, generally one potato per person. If you are using instant potatoes, then figure one cup of cooked potatoes per person.
It depends what else they are having. If a 3 veg and meat dinner, I would serve 4 oz au gratin per. -This will take 50 pounds potato.
~27.34
If you are making the potato salad, start with the potatoes. 25 pounds of potatoes will make moderate servings for 100.40 pounds will make generous servings for 100, but can easily serve 120.If the potato salad is pre-made, you will need 4 to 4 1/2 gallons to serve 100.
To serve 300 people, you will need about 9.375 gallons of potato salad. This is based on one gallon being 16 cups, so, if you figure 1/2 cup per serving, one gallon should serve 32 people.
I have done this! Wrap your potatoes in aluminum foil and place in electric roasters. You can get about 30-35 potatoes in each roaster. I started them at 400 at 7:00 am. About 8:30, we took the ones on the outside and place the inside ones on the outside. and put the outside ones on the inside. We then kept watching them and switching some around. They were done by 11:00 a.m.
so it would not get cold
I would serve 4 oz per person. So 5 pounds for 20 people.