Question: how long do you cook roast beef per kg?
Answer: Reduce the heat to 190C/375F/Gas 5 and roast for half an hour per kilo for rare, adding another ten minutes per kilo for medium rare, 20 minutes per kilo for medium, and 30 minutes per kilo for well done. Remove the beef from the oven, transfer it to a carving board and cover with foil.