How many potatoes are needed to make 10 servings of mashed potatoes?

It may sound excessive at first, but for 10 people, I would go ahead and peel and prepare the full ten pound bag of potatoes. Some of that ten pounds is water, and a little bit is peel, so you don't end up with 10 lbs of mashed potatoes. I routinely prepare that volume of potatoes, and what you end up with is a very large bowl full of potatoes, true, but that allows both for mashed potatoes for ten, but hopefully, seconds for those who want them.