The correct temperature for cooking prime rib is 450 degrees Fahrenheit for the first 30 to 45 minutes, then 325 degrees Fahrenheit for the remaining cooking time. Cooking time varies depending on desired rarity and quantity of meat.
For rare meat, the internal temperature must reach 120 degrees Fahrenheit. Two ribs only require roughly an hour of cooking time to reach an internal temperature of 120 to 125 degrees Fahrenheit, but seven ribs require closer to four hours, or about 15 minutes per pound.
More-well-done meat requires extra cooking time. Medium-rare meat requires an internal temperature of 130 to 135 degrees Fahrenheit, while medium meat requires an internal temperature of 140 to145 degrees Fahrenheit. For medium-well-done meat, the internal temperature must reach150 to 155 degrees Fahrenheit, and well-done meat requires an internal temperature of 160 degrees Fahrenheit. The outside of the meat is usually more well done than the inside.