Prime Rib (Standing Rib Roast)
at 325°F
3 hr 5 min – 4 hr Plan on 23 to 30 minutes per pound in a 325°F oven. A 8 lb prime rib (standing rib roast) lands around 3 hr 5 min – 4 hr. Done is 145°F on a food thermometer, plus a 20-minute rest — never the clock alone.
Time by weight at 325°F
Planning ranges for a fully thawed, fridge-temperature prime rib (standing rib roast). The right-hand column is when to take the first thermometer reading.
| Weight | Estimated time at 325°F | Check thermometer from |
|---|---|---|
| 4 lb | 1 hr 30 min – 2 hr | 1 hr 20 min in |
| 5 lb | 1 hr 55 min – 2 hr 30 min | 1 hr 40 min in |
| 6 lb | 2 hr 20 min – 3 hr | 1 hr 55 min in |
| 7 lb | 2 hr 40 min – 3 hr 30 min | 2 hr 15 min in |
| 8 lb | 3 hr 5 min – 4 hr | 2 hr 35 min in |
| 9 lb | 3 hr 25 min – 4 hr 30 min | 2 hr 55 min in |
| 10 lb | 3 hr 50 min – 5 hr | 3 hr 15 min in |
| 11 lb | 4 hr 15 min – 5 hr 30 min | 3 hr 35 min in |
| 12 lb | 4 hr 35 min – 6 hr | 3 hr 55 min in |
Start checking the internal temperature well before the low end of the range — an early check costs nothing; a late one costs the meal. Done means 145°F on a food thermometer.
325°F vs the other temperatures
Same cut, every temperature this site publishes for it.
| Oven temp | Time for a 8 lb prime rib (standing rib roast) | Per pound |
|---|---|---|
| 325°F (this page) | 3 hr 5 min – 4 hr | 23–30 min/lb |
| 350°F | 2 hr 40 min – 3 hr 30 min | 20–26 min/lb |
When is it actually done?
145°F internal The USDA FSIS safe minimum internal temperature for this cut is 145°F, followed by a rest of about 20 minutes. The clock estimates; the thermometer decides. Every time on this page is a planning range, not a doneness test.
Doneness temperatures
| Doneness | Internal temp | |
|---|---|---|
| Rare | 120–125°F | below the USDA minimum |
| Medium-rare | 130–135°F | below the USDA minimum |
| Medium | 135–145°F | |
| Medium-well | 145–155°F | |
| Well done | 155°F+ |
USDA FSIS recommends a minimum of 145°F with a 20-minute rest for whole cuts. Rare and medium-rare sit below that guideline — a personal choice many cooks make with fresh, well-handled meat, listed here because these are the temperatures cookbooks and restaurants use.
Worth knowing before you start
- The low end of each range lands medium-rare, the high end medium — decide your pull temperature before you start, not at the oven door.
- A large roast carries over 5–10°F while resting; pull it that far below your target.
- Many cooks finish with a 500°F blast for the last 8–10 minutes (or start with one) for the crust — the per-pound time barely changes.
- Bones act as insulation: a boneless ribeye roast of the same weight cooks slightly faster.
Answers people ask
How long does a bone-in prime rib take at 325°F?
Plan on 23 to 30 minutes per pound at 325°F. A 8 lb example takes about 3 hr 5 min – 4 hr. It is done when the internal temperature reaches 145°F on a food thermometer, not when the clock runs out.
What internal temperature is a bone-in prime rib done at?
145°F, measured with a food thermometer in the thickest part, then rested about 20 minutes. That is the USDA FSIS safe minimum.
Is 325°F a good temperature for a bone-in prime rib?
It is one of 2 temperatures this site publishes for this cut (325°F, 350°F). It is the most commonly used.
Where these numbers come from
Ranges are anchored to USDA FSIS published timetables where they exist, and derived from that anchor plus cross-checked published sources where they do not — widened to cover the disagreement between sources rather than split down the middle. The full reasoning is on the method page. If a figure here looks wrong, say so — corrections are prioritised.