Prime rib, also referred to as standing rib roast, is a beautiful piece of meat. A well-cooked prime rib is juicy, full of flavor, and not at all difficult to make. How long do I have to cook prime rib? Medium-rare — 110ºMedium — 120ºMedium-well — 130ºWell — 140ºHow do I cook a prime rib roast to medium rare? Cooking a prime rib to medium rare is our preferred doneness—it has a red, warm center.