Mashed Potatoes For 15 People. If mashed potatoes are the main dish, then the serving sizes may need to be doubled. Most people eat about 6 ounces of potatoes per side dish but mashed potatoes are a favorite so expect serving sizes to be just a bit larger, at around 6.5 to 8 ounces.

Cover with foil and bake at 350 degrees for 25 minutes. In this way, how many pounds roast potatoes per person? To reheat frozen mashed potatoes, place frozen mashed potatoes in a casserole dish.