How many pounds of pot roast to feed 100 people?

Taking into consideration that the pot roast will be served with other sides, such as mashed potatoes, veggies, and whatnot, the average person would probably eat only a quarter to half a pound, so approximately 25-45 pounds of meat. I would recommend preparing extra sides and another option than just pot roast because a) options are always good, and b) you will probably want to get extra meat just in case your guests eat more than half a pound.