How long a roast needs to cook depends on what type of meat you are cooking. Beef will have a different cooking time than a pork roast. In some cases, even the cut of meat affects cooking time, as bone-in and boneless cuts cook at different rates. General guidelines for cooking times are available in most cookbooks and through the USDA's Food Safety and Inspection service. Add this to my Recipe Box.
Beef Roasts
Beef roasts are cooked between rare and well done depending on the cut of meat. Most prime rib is served either rare or medium rare, while a brisket roast is most often cooked to well done. When cooking a beef roast, a meat thermometer is your best bet for determining the doneness of meat. Without one, you can judge by cooking time for the cut. A 4-pound, bone-in rib roast will take approximately 1 3/4 hours to reach the medium rare stage, while you would need to add another 20 minutes for a boneless rib roast. Rump or round roasts will take about 2 hours to cook to medium, and add an additional 20 minutes for well done. A boneless tenderloin roast will take approximately 4 hours to cook in the oven. Cooking times for braising or Dutch oven cooking are about the same if cooked over medium heat.
Pork Roasts
Most 4-pound pork roast cuts can be roasted for two hours and be considered done. This includes crown, tenderloin and loin roasts. Boston butt roasts are the exception, needing a longer cooking time at around three hours. Hams, both fresh and smoked, need between 1 3/4 and 2 1/2 hours. Pork should be cooked to an internal temperature of 160 degrees Fahrenheit to be considered fully cooked and safe to eat.
Lamb or Goat Roasts
Lamb and goat are considered to be red meats and therefore can be cooked to varying degrees of doneness. For a 4-pound lamb roast, you should cook the meat for 2 1/3 hours for medium rare, three hours for medium and 3 1/3 hours for well done. Subtract 30 minutes for boneless roasts. Goats are cooked much like lamb and can be substituted in most recipes. Goat roasts should be cooked to an internal temperature of 160 degrees Fahrenheit, and this will take a 4-pound goat roast approximately three to 3 1/2 hours.
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