Note from Ricardo A 2.5 lb (1.2 kg) rib roast generally makes three to four portions. If you want to prepare leftover roast beef sandwiches, serve this roast for three people. You can then prepare two or three sandwiches. For six people, buy two roasts of 2.5 lb (1.2 kg) each. A rib roast is not as tender as a tenderloin roast, but it is a very flavourful roast.