I usually shoot for about ½ to ¾ cup of potatoes per person. 1 cup of potatoes weighs about 5 ounces (rounded up). I like to buy 5 ounces for each person so that I'm sure to have leftovers. When you're buying potatoes at the store, you can guesstimate that you'll need 3 to 4 ounces of potatoes per person.