How to Know: How Long Do You Cook Roast Beef

Select a good cut of beef. You can use beef tenderloin, a sirloin or fillet to make roast beef. If you are budget conscious, a rump roast is a good choice. The texture is a little coarse and chewy, but the flavor is excellent. A rump roast is about half the cost of a tenderloin. Whatever beef you are cooking, make sure it has a dark color and marbling throughout. Marbling is the white fat you can see running through uncooked meat. Fat adds flavor to the meat, so make sure your meat also has a covering of fat. This will keep your meat juicy and add flavor.

Season the meat. This is optional when cooking your roast, but you may want to marinade the roast or dry rub it. Marinades involve some kind of citric acid to tenderize the meat, and can help a cheaper cut of meat come out less tough. White wine, lemon juice and vinegar can all be used to marinade your meat. You can leave your meat in the marinade from 1/2 hour to 24 hours. A dry rub consists of seasonings such as salt, black pepper and rosemary. Coat the meat in the dry rub right before you cook it to add flavor to your meat.

Cook the roast. Preheat your oven to 425 degrees. Place the beef in a roasting pan with the fat side facing up. Put the meat thermometer into the thickest part of the meat. Put the roast in the oven, uncovered. Cook it at 425 for 1/2 hour. Lower the temperature to 325 for the remainder of the cooking time. Your cooking time will vary depending on how you like your meat done.

Remove the roast from the oven when it is done to your liking. Read the temperature on the meat thermometer to gauge how well done the meat is. If you like rare roast beef, remove the roast from the oven when the meat is at 140 degrees. For medium, remove it when the temperature is 160 degrees. For well done, remove it when the temperature is 175 degrees.

Let the roast rest. Resting your meat will allow fibers and gristle to soften, and will release juices you can use to make gravy. Once you have removed the roast from the oven, loosely cover it with tinfoil and let it rest for up to an hour.