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Prime Rib Cooking Time: How Long per Pound?
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A bone-in prime rib of 4 to 8 pounds roasts in about 23 to 30 minutes per pound at 325 °F: about 2 hours 18 minutes to 3 hours for 6 pounds. Cook it to at least 145 °F, the USDA safe minimum for beef roasts, then let it rest for 3 minutes or more before carving.
Roast a bone-in prime rib (standing rib roast) of 4 to 8 pounds at 325 °F (163 °C) for about 23 to 30 minutes per pound. A 6 pound roast takes about 2 hours 18 minutes to 3 hours. A boneless rib roast of about 4 pounds takes longer per pound: 39 to 43 minutes.
The USDA’s safe minimum for beef roasts is 145 °F (63 °C), measured with a food thermometer in the thickest part away from the bone, followed by a rest of at least 3 minutes. The minutes per pound only get you close: the thermometer decides when it is done.
Prime rib cooking time by weight
Bone-in rib roast at 325 °F, using the USDA range of 23 to 30 minutes per pound:
| Roast weight | In kilograms | Total time at 325 °F |
|---|---|---|
| 4 lb | 1.8 kg | 1 h 32 min to 2 h |
| 5 lb | 2.3 kg | 1 h 55 min to 2 h 30 min |
| 6 lb | 2.7 kg | 2 h 18 min to 3 h |
| 7 lb | 3.2 kg | 2 h 41 min to 3 h 30 min |
| 8 lb | 3.6 kg | 3 h 04 min to 4 h |
Bone-in or boneless?
The bones conduct heat and shield the meat, so a bone-in roast cooks in fewer minutes per pound than a boneless one. Boned and rolled cuts take longer per pound because the heat has to travel through solid meat. For a boneless rib roast of about 4 pounds, allow 39 to 43 minutes per pound: roughly 2 hours 36 minutes to 2 hours 52 minutes.
Step by step
- Set the oven to 325 °F; the USDA does not recommend cooking meat below 325 °F.
- Put the roast fat side up on a rack in a shallow, uncovered pan.
- Start checking the temperature 30 minutes before the shortest time in the chart.
- Take it out at 145 °F or higher and let it rest for at least 3 minutes before carving; the inside keeps warming a little as it rests.
Is prime rib always “Prime” beef?
Not necessarily. “Prime rib” is the name of the cut, the rib roast, while USDA Prime is a quality grade. Many prime rib roasts sold in stores are USDA Choice. Both roast the same way; Prime has more marbling.
Converting for metric ovens
325 °F is 163 °C (gas mark 3) and 145 °F is 63 °C. One pound is 0.4536 kg; use the weight converter for your roast and the temperature converter for any other temperature.
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Step by step: Prime Rib Cooking Time per Pound
- Weigh the roast and note whether it is bone-in or boneless.
- Multiply the weight by 23 to 30 minutes (bone-in) or 39 to 43 minutes (boneless).
- Roast uncovered at 325 °F, fat side up, on a rack.
- Check with a thermometer and take it out at 145 °F or higher, then rest it 3 minutes.
Quick reference
°F to °C
| °F | °C |
|---|---|
| 0.5 °F | -17.5 °C |
| 1 °F | -17.222222 °C |
| 2 °F | -16.666667 °C |
| 5 °F | -15 °C |
| 10 °F | -12.222222 °C |
| 25 °F | -3.888889 °C |
| 50 °F | 10 °C |
| 100 °F | 37.777778 °C |
| 250 °F | 121.111111 °C |
| 1,000 °F | 537.777778 °C |
Accuracy
How we checked this
We compared 4 results from this calculator with values we worked out independently, using exact decimal arithmetic and the published definitions, on October 26, 2026. 4 of 4 matched to the precision shown.
| Input | Independent value | This page | Match |
|---|---|---|---|
| 100 °C → °F | 212 | 212 | Yes |
| 98.6 °F → °C | 37 | 37 | Yes |
| 0 K → °C | -273.15 | -273.15 | Yes |
| -40 °C → °F | -40 | -40 | Yes |
From the source
Cook raw beef, lamb, pork, and veal steaks, roasts, and chops to a minimum internal temperature of 145 °F.
Sources
GOOD TO KNOW
Frequently asked questions
How long do you cook a 5 pound prime rib?
About 1 hour 55 minutes to 2½ hours at 325 °F for a bone-in roast (23 to 30 minutes per pound), until it reaches at least 145 °F.
What temperature should prime rib be?
The USDA’s safe minimum for beef roasts is 145 °F (63 °C), measured in the thickest part, with a rest of at least 3 minutes.
Do you cook prime rib covered or uncovered?
Uncovered, on a rack in a shallow pan, fat side up.
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