Set the Timer

• Doubling the size of the roast does usually increase the cooking time. Plan on a larger roast taking about twice as long. To estimate the cooking time for any roast, calculate the time by how long the roast takes per pound to cook. For example, a boneless prime rib takes approximately 25 to 30 minutes per pound, while a sirloin or rump roast takes between 30 to 35 minutes per pound. A 5-pound prime rib needs approximately two to three hours to cook; a 10-pound roast needs five hours.

Cooking Temperature

• How long a roast takes to cook depends not only on its size, but on the oven's temperature. Slow roasting at 275 degrees Fahrenheit takes 30 to 40 percent more time than roasting meat at higher heat -- between 325 and 350 F. Don't let the timing determine your roasting method, though. In most cases, roasts taste best when cooked slowly, followed by a brief blast of high heat to caramelize the outside of the meat. Slow-roast prime rib, sirloin, chuck roast and top round. The one exception to this rule is tenderloin, which tastes best when cooked quickly at high heat.

Dinner's Ready

• Cooking times are only estimates when it comes to roasting beef. Actual cooking times can vary considerably due to the thickness of the meat, the temperature the meat was when you put it in the oven and even your oven's eccentricities. The most reliable way to cook a roast is by using a meat thermometer to test for doneness. Beginning 30 minutes to an hour before you think the roast will be done, insert a meat thermometer into the thickest portion of the roast. Although the U.S. Department of Agriculture recommends an internal temperature of 145 F as the minimum safe temperature for cooked roast, many people prefer their beef rarer. At 120 F, the meat is considered rare. It is very rare and just warm in the center. A temperature of 125 F is considered medium. At this temperature, the roast will be pink, but juicy. A roast is well done when the thermometer registers 140 F. Well done roast will be slightly pink and very warm. No matter what the clock says, pull the roast from the oven when it reaches the degree of doneness you prefer.

Let It Be

• Don't forget to add prep time and resting time to your calculations when preparing a roast. For the most flavorful roasts, unwrap the roast a day or two in advance. Salt the roast well. Cover and refrigerate it. Pull the roast from the refrigerator an hour before you plan to cook it and let it set on the counter top to come to room temperature. Salting the meat ahead of time adds flavor and moisture, while allowing it to come to room temperature ensures more even and faster cooking. After the roast reaches its ideal temperature, set it in a draft-free spot for 20 to 30 minutes before you slice it. This resting period allows the juices to settle so the roast slices more easily and tastes juicier.