Enter the weight of your standing rib roast and the doneness you want to see how long it needs at 325°F (163°C), what temperature to take it out of the oven, and when to start so it is ready at dinner time. Times are the usual rule of thumb for a bone-in roast; your thermometer has the final say.
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Food-safety note: the USDA safe minimum for whole cuts of beef is 145°F (63°C) with a 3 minute rest. Rare and medium-rare prime rib are cooked below that, a matter of taste and risk; the outside of a whole roast is the part exposed to bacteria and gets well cooked. Choose a higher doneness for children, pregnant women, older people or anyone with a weak immune system.
| Doneness | Take out of the oven | Final after resting | Minutes per pound at 325°F |
|---|---|---|---|
| Rare | 115–120°F (46–49°C) | 120–125°F (49–52°C) | about 15 |
| Medium-rare | 120–125°F (49–52°C) | 130–135°F (54–57°C) | about 17 |
| Medium | 130–135°F (54–57°C) | 140–145°F (60–63°C) | about 20 |
The roast keeps cooking while it rests, and the temperature in the center usually rises another 5 to 10°F (3 to 6°C). That is why you pull it before the final temperature.
| Weight | Approx. time (17 min/lb) | Servings |
|---|---|---|
| 4 lb (1.8 kg), 2 ribs | 1 h 8 min | 2 to 4 |
| 6 lb (2.7 kg), 3 ribs | 1 h 42 min | 4 to 6 |
| 8 lb (3.6 kg), 4 ribs | 2 h 16 min | 6 to 8 |
| 10 lb (4.5 kg), 5 ribs | 2 h 50 min | 8 to 10 |
| 12 lb (5.4 kg), 6 ribs | 3 h 24 min | 10 to 12 |
About 2 hours 16 minutes at 325°F for medium-rare (17 minutes per pound), roughly 2 hours for rare and 2 hours 40 minutes for medium. Use a thermometer to know for sure.
Take it out at 120°F to 125°F (49°C to 52°C) for medium-rare; it will rise to 130°F to 135°F (54°C to 57°C) while resting. The USDA safe minimum for beef roasts is 145°F (63°C).
At 325°F, about 15 minutes per pound for rare, 17 for medium-rare and 20 for medium. These are rules of thumb, not guarantees.
20 to 30 minutes, loosely covered with foil. The juices redistribute and the roast is easier to carve.
One rib per two people for a bone-in roast (about 1 pound per person with bone), or about ½ to ¾ pound per person boneless.
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