The amount of roast beef necessary for feeding each person at a dinner party varies depending on the type of cut. For a semi-boneless rib roast, purchase about one rib per person. For a whole beef tenderloin or a boneless rib eye roast, purchase about 1/2 pound per person.
A peeled beef tenderloin requires about 1/3 pound per person. A New York strip, sirloin or top roast requires about 1/2 pound per person. Each serving equates to about 3 ounces of cooked meat per person, which is the recommended serving size. For holiday functions, it is important to cook more than needed to account for seconds helpings.