How Long to Cook a 12 lb Prime Rib (Medium)
A 12 lb prime rib needs about 8h 25m at 250 °F / 120 °C for medium. Pull it at 134 °F / 57 °C so carryover takes it to 140 °F, then rest 40 min before carving.
Every method compared
Same 12 lb prime rib, same doneness — only the heat changes. The Christmas roast, and an expensive one to overcook. Low and slow to within 10 °F of target, then a blast of heat for the crust.
| Method | Pit temp | Cook time | Pull at | Rest |
|---|---|---|---|---|
| Reverse Sear | 250 °F / 120 °C | 8h 25m | 134 °F | 40 min |
| Smoker (Low & Slow) | 225 °F / 110 °C | 9h 35m | 135 °F | 40 min |
Pull temps differ per method on purpose: a 450 °F grill drives far more residual heat into the meat than a 225 °F pit, so the same final temperature needs a different pull point.
Prime Rib (Standing Rib Roast) temperature chart
| Doneness | Final temp | Pull at (12 lb) | Looks like |
|---|---|---|---|
| Rare | 125 °F / 52 °C | 119 °F | Cool red center, very soft. |
| Medium Rare | 130 °F / 55 °C | 124 °F | Warm red center — the sweet spot for most steaks. |
| Medium | 140 °F / 60 °C | 134 °F | Warm pink center, firmer bite. |
| Medium Well | 150 °F / 65 °C | 144 °F | Slight pink, noticeably drier. |
Recommended Tools for Perfect Results
You cannot cook to temperature without measuring temperature. These are the two tools that change results the most.
Wireless Bluetooth Meat Thermometer
Leave-in probe with phone alerts. The single upgrade that ends dry brisket and grey steak.
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Pink Butcher Paper (Unwaxed, 18")
Beats foil for the Texas Crutch: pushes through the stall while keeping the bark crisp.
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Instant-Read Digital Thermometer
Two-second readings for spot checks and for probing brisket for tenderness.
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Other doneness levels at 12 lb
Other sizes
Download the printable temperature chart
Every temperature on this site on one page — beef, pork, poultry, seafood and low & slow, plus the carryover rule. Print it and tape it inside your grill lid.
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Frequently Asked Questions
How long does a 12 lb prime rib take?
About 8 hours 25 minutes at 250 °F, plus 40 minutes of rest. Weight is only a guide — start probing early, because roast shape matters as much as weight.
What internal temperature should it reach?
140 °F / 60 °C final. Pull it at 134 °F: a roast this size carries over about 6 °F while resting.
How long should it rest?
40 minutes. Tent it loosely with foil — a large roast holds heat for a surprisingly long time.