How Long to Cook Prime Rib
Standing rib roast, bone-in. A premium holiday roast.
The Short Answer
The USDA-recommended safe internal temperature is 145°F, verified with an instant-read thermometer in the thickest part. Scroll down for all cooking methods, detailed instructions, and tips from the Professor.
Always verify with an instant-read thermometer inserted into the thickest part.
Cooking Methods
🔥 Oven
Temperature: 250°F
Rest: 30 minutes
Low and slow at 250°F until internal temp reaches 120°F for medium-rare. Then rest, then sear at 500°F for 8-10 minutes for the crust. Time varies by weight.
Time by Weight
| Weight | Cook Time |
|---|---|
| 4–6 lbs | 2–2.5 hours |
| 6–8 lbs | 2.5–3 hours |
| 8–10 lbs | 3–3.5 hours |
| 10–12 lbs | 3.5–4 hours |
Pull the roast when the internal temperature is 10 degrees BELOW your target. Carryover cooking during the 30-minute rest will bring it up. This is the most common mistake with prime rib.
Frequently Asked Questions
At 250°F, approximately 3 to 3.5 hours for medium-rare. Always use a thermometer; time estimates are approximate because oven temperatures and roast shapes vary.
The Bottom Line
Prime Rib is straightforward to cook when you know the time and temperature. The most important number to remember is 145°F internal. An instant-read thermometer is the only reliable way to confirm doneness; color and firmness are not accurate indicators. Use the method that fits your equipment and schedule, and always let the food rest before cutting or serving. Resting allows juices to redistribute and carryover cooking to finish the job.
Source: USDA Safe Minimum Internal Temperatures | Last verified: March 19, 2026 | Our methodology