Butchers generally recommend buying extra as people's consumption can vary. Buy a little more than needed and you can use the leftovers to create incredible dishes. When buying boneless cut of beef, on average most people will consume between six and eight ounces per meal. If buying bone-in beef, allocate 12 ounces per person.  When calculating the amount, keep in mind it's based on a raw, uncooked cut of roast beef.