how long cook roast beef
4 Cook the roast initially at 375Â°F (190Â°C) for half an hour, to brown it. Then lower the heat to 225Â°F (107Â°C). The roast should take somewhere from 1 1/2 to 2 1/2 hours additionally to cook. The shape of the roast will affect the cooking time.If your roast is long and narrow, rather than a more round shape, it may take less time to cook, so keep an eye on it. When juices start to drip from the roast, and it is browned on the outside, check the roast's internal temperature with a meat thermometer. Cook the roast initially at 375Â°F (190Â°C) for half an hour, to brown it. Then lower the heat to 225Â°F (107Â°C). The roast should take somewhere from 1 1/2 to 2 1/2 hours additionally to cook. The shape of the roast will affect the cooking time.