The cooking time for a prime rib roast can vary depending on the size of the roast and the desired level of doneness. As a general guideline, you can estimate approximately 15 to 20 minutes per pound (0.45 kg) for cooking a prime rib at 350°F (175°C) for medium-rare doneness.
To get a more accurate cooking time, it is recommended to use a meat thermometer. Insert the thermometer into the thickest part of the roast without touching the bone, and cook until the internal temperature reaches your desired level of doneness. Here are the recommended internal temperatures for prime rib:
- Rare: 120-125°F (49-52°C)
- Medium-rare: 130-135°F (54-57°C)
- Medium: 140-145°F (60-63°C)
- Medium-well: 150-155°F (66-68°C)
- Well done: 160°F (71°C) or higher
Keep in mind that these temperatures are guidelines, and personal preferences may vary. It's always best to use a meat thermometer to ensure the roast is cooked to your desired level of doneness. Additionally, it's a good practice to let the roast rest for 15-20 minutes before carving to allow the juices to redistribute.