I like to plan on 6 ounces, or just under 1/2 pound per person when calculating how much meat to buy for dinner. This is for when the loin is the star and main attraction of the meal and I am serving a single starch and a single vegetable side dish. If I am serving multiple side dishes along with salad and bread, I will calculate for 4 ounces per person. When I buy a whole beef tenderloin I am going to get multiple meals for special occasions out of it for my family of 5.