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About the prime rib cooking time calculator
Type the weight of your prime rib, choose bone-in or boneless, and pick how you like it: rare, medium rare, medium, medium well or well done. The calculator tells you how long to roast it, the inside temperature at which to take it out, how warm it gets while it rests, and how many people it feeds.
A prime rib keeps cooking after it leaves the oven: the inside rises about 5–10 °F (3–6 °C) while it rests. So you take it out a little before it reaches the doneness you want.
Food safety: the USDA Food Safety and Inspection Service (FSIS) says beef roasts are safe at 145 °F (63 °C), measured before you take the meat out of the oven, with a rest of at least 3 minutes. Rare, medium rare and medium prime rib are below that minimum. The calculator shows the USDA minimum next to every doneness, so you can choose.
Features
- 5 doneness levels — rare to well done, with the temperature to take it out and the temperature after resting
- Bone-in or boneless — a standing rib roast or a rib-eye roast
- Total time and minutes per pound — or per kg
- 325 °F or 350 °F — the USDA chart is for 325 °F; 350 °F is our estimate
- The USDA minimum shown — 145 °F with a 3-minute rest, next to every doneness
- Ribs and servings — tap a number of ribs to set the weight; see how many people it feeds
- A table — every doneness with its time for your roast
Prime rib temperature chart
These are cook's guide temperatures, not USDA figures. Take the roast out at the first temperature; it climbs to the second while it rests.
| Doneness | Take it out at | After resting | USDA minimum (145 °F + 3 min) |
|---|---|---|---|
| Rare | 115 °F (46 °C) | 120–125 °F (49–52 °C) | below |
| Medium rare | 125 °F (52 °C) | 130–135 °F (54–57 °C) | below |
| Medium | 135 °F (57 °C) | 140–145 °F (60–63 °C) | below |
| Medium well | 145 °F (63 °C) | 150–155 °F (66–68 °C) | meets it |
| Well done | 155 °F (68 °C) | 160 °F (71 °C) and up | meets it |
How the time is worked out
The USDA FSIS Holiday Meat Roasting Chart gives a bone-in rib roast of 4–8 lb at 325 °F 23–30 minutes per pound, and a boneless rib roast of 4 lb 39–43 minutes per pound — both to 145 °F.
For other doneness levels and for 350 °F, the calculator scales these times with a simple heat formula: the time grows with ln((oven − 40) ÷ (oven − take-out temperature)), for meat that starts at fridge temperature (40 °F). This is our estimate, not a USDA figure.
| Doneness | Bone-in at 325 °F | Bone-in at 350 °F | Boneless at 325 °F |
|---|---|---|---|
| Rare | 15–20 min per lb | 14–18 min per lb | 26–29 min per lb |
| Medium rare | 18–23 min per lb | 16–21 min per lb | 30–33 min per lb |
| Medium | 20–26 min per lb | 18–24 min per lb | 34–38 min per lb |
| Medium well | 23–30 min per lb | 21–27 min per lb | 39–43 min per lb |
| Well done | 26–34 min per lb | 23–30 min per lb | 44–48 min per lb |
Prime rib cooking times by weight
Bone-in, at 325 °F. A rib is about 2 lb.
| Weight | Ribs | Medium rare | Medium |
|---|---|---|---|
| 4 lb (1.8 kg) | 2 | 1 h 10 min – 1 h 30 min | 1 h 20 min – 1 h 45 min |
| 6 lb (2.7 kg) | 3 | 1 h 45 min – 2 h 20 min | 2 h – 2 h 40 min |
| 8 lb (3.6 kg) | 4 | 2 h 20 min – 3 h 5 min | 2 h 40 min – 3 h 30 min |
| 10 lb (4.5 kg) | 5 | 2 h 55 min – 3 h 50 min | 3 h 25 min – 4 h 25 min |
| 12 lb (5.4 kg) | 6 | 3 h 35 min – 4 h 35 min | 4 h 5 min – 5 h 20 min |
Start checking with the thermometer at the short time. A roast that is wide and flat cooks faster than a tall one.
Worked example
The page opens on an 8 lb bone-in prime rib, medium rare, at 325 °F.
- Minutes per pound: 23–30 × 0.771 = 18–23 min per lb
- Time: 8 × 17.7 = 142 min, 8 × 23.1 = 185 min, so 2 h 20 min – 3 h 5 min
- Take it out at 125 °F (52 °C); after resting it is about 130–135 °F (54–57 °C)
- Rest it 20–30 minutes, loosely covered with foil
- It feeds about 8–10 people (¾–1 lb of bone-in roast each) — about 4 ribs
- The USDA minimum is 145 °F (63 °C) with a 3-minute rest; medium rare is below it
Frequently asked questions
How long do I cook a prime rib per pound?
At 325 °F, about 18–23 minutes per pound for medium rare and 20–26 minutes for medium, bone-in. The USDA chart gives 23–30 minutes per pound to reach 145 °F. Boneless roasts take longer per pound.
At what temperature do I take prime rib out of the oven?
For medium rare, at about 125 °F (52 °C). It rises to 130–135 °F while it rests. For medium, take it out at 135 °F (57 °C).
What is the USDA safe temperature for prime rib?
The USDA FSIS says beef steaks and roasts are safe at 145 °F (63 °C), measured before you take them off the heat, with a rest of at least 3 minutes. Rare, medium rare and medium are below this.
How long should prime rib rest?
20–30 minutes, loosely covered with foil. The juices settle and the slices stay moist. The USDA asks for at least 3 minutes.
Bone-in or boneless?
A boneless roast needs more minutes per pound. The USDA explains that heat takes longer to get through solid, rolled meat. A bone-in roast (a standing rib roast) stands on its bones in the pan; a boneless roast is easier to carve.
How much prime rib per person?
Plan about ¾–1 lb of bone-in roast or ½ lb of boneless roast per person. One rib feeds about 2 people.
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How to use it
- Choose Bone-in (standing rib roast) or Boneless (rib-eye roast)
- Type the Weight of the roast, or tap a number of Ribs. Change the Unit to kg if you like
- Pick how you like it: Rare, Medium rare, Medium, Medium well or Well done
- Pick the Oven temperature: 325 °F (the USDA chart) or 350 °F
- Read the time, the temperature to take it out, and the USDA minimum
- Check the center with a meat thermometer, rest the roast, and press Copy to keep the result
