Prime Rib Cooking Time Calculator (by Weight and Doneness)
Roast time by weight, the temperature to pull it at, and when to start.
250 °F (121 °C) takes longer but cooks more evenly from edge to center.
- Estimated roast time
- 1 hr 26 min – 1 hr 59 min
- Oven temperature
- 163°C
- Pull at (internal)
- 52°C–54°C
- Medium-rare after resting
- 57°C
- Rest before carving
- 20–30 min
- Weightbone-in
- 3 kg
- Cook to temperature, not time: start checking the center at 1 hr 26 min with a probe thermometer, away from the bone.
- At 163°C the roast keeps cooking while it rests, so pull it 3–6 °C below your target.
- USDA’s safe minimum for beef roasts is 63°C with a 3-minute rest. Rare and medium-rare are below that line.
What is the Prime Rib Cooking Time Calculator?
This prime rib calculator estimates roasting time from the roast’s weight, bone-in or boneless, and the doneness you want. Pick a classic 325 °F roast or America’s Test Kitchen’s low-and-slow 250 °F method, and it gives you the time range, the internal temperature to pull the roast at, and the temperature it should reach after resting. Enter your serve time and it works backwards to tell you when the roast goes in. The times come from USDA, butcher Pat LaFrieda and America’s Test Kitchen, and it works in US or metric units.
How to use the Prime Rib Cooking Time Calculator
- 1 Enter the roast’s weight and whether it’s bone-in or boneless.
- 2 Choose your doneness and oven method.
- 3 Optionally set your serve time to get an oven-in time.
- 4 Roast to the pull temperature shown, then rest 20–30 minutes before carving.
Prime rib cooking time chart by weight
Estimated roasting times for a bone-in rib roast from the fridge, using the same figures as the calculator above: Pat LaFrieda’s 13–18 minutes per pound for medium-rare at 325 °F, USDA’s 23–25 minutes per pound to 145 °F, and America’s Test Kitchen’s 3–3½ hours for a 7 lb roast at 250 °F, scaled by weight. Add 20–30 minutes of resting.
| Roast weight | 325 °F, medium-rare | 325 °F, medium | 250 °F, low & slow |
|---|---|---|---|
| 4 lb (1.8 kg) | 52 min – 1 hr 12 min | 1 hr 32 min – 1 hr 40 min | 1 hr 43 min – 2 hr |
| 5 lb (2.3 kg) | 1 hr 5 min – 1 hr 30 min | 1 hr 55 min – 2 hr 5 min | 2 hr 9 min – 2 hr 30 min |
| 6 lb (2.7 kg) | 1 hr 18 min – 1 hr 48 min | 2 hr 18 min – 2 hr 30 min | 2 hr 34 min – 3 hr |
| 7 lb (3.2 kg) | 1 hr 31 min – 2 hr 6 min | 2 hr 41 min – 2 hr 55 min | 3 hr – 3 hr 30 min |
| 8 lb (3.6 kg) | 1 hr 44 min – 2 hr 24 min | 3 hr 4 min – 3 hr 20 min | 3 hr 26 min – 4 hr |
| 10 lb (4.5 kg) | 2 hr 10 min – 3 hr | 3 hr 50 min – 4 hr 10 min | 4 hr 17 min – 5 hr |
| 12 lb (5.4 kg) | 2 hr 36 min – 3 hr 36 min | 4 hr 36 min – 5 hr | 5 hr 9 min – 6 hr |
- Cook to temperature, not to time. Pull the roast 5–10 °F (3–6 °C) below your target at 325 °F; at 250 °F it barely rises, so pull at the target.
- Boneless roasts take longer per pound: USDA’s chart allows 28–33 minutes per pound against 23–25 for bone-in. Switch the calculator to Boneless for those times.
- USDA’s chart covers 4–6 lb roasts and America’s Test Kitchen tested a 7 lb roast. Times for bigger roasts are scaled by weight, so start checking early.
Frequently asked questions
How long do you cook prime rib per pound? +
At 325 °F (163 °C), butcher Pat LaFrieda allows 13–18 minutes per pound for medium-rare, starting from a fridge-cold roast. USDA’s chart gives 23–25 minutes per pound for a bone-in rib roast cooked to 145 °F (medium). Either way, start checking early and go by the thermometer.
What temperature should I pull prime rib at? +
Certified Angus Beef says to take a roast out 5–10 °F below the doneness you want, because it keeps rising while it rests: about 125–130 °F for medium-rare (135 °F after resting). At 250 °F the rise is small, so America’s Test Kitchen pulls at 130 °F for medium-rare.
Is rare or medium-rare prime rib safe? +
USDA’s safe minimum for beef roasts is 145 °F (63 °C) with at least a 3-minute rest. Rare and medium-rare are below that line, so the choice is yours; anyone who is pregnant, elderly or immune-compromised should eat it cooked to 145 °F.
How accurate are the results? +
The figures come from standard, tested references (USDA FoodData Central and King Arthur Baking) and are excellent starting points. Ovens, ingredients and equipment vary, so treat the numbers as a reliable guide and adjust to taste and doneness.
Is this calculator free, and does it send my data anywhere? +
Yes — it’s completely free and runs entirely in your browser. Nothing you type is uploaded or stored on a server; the maths happens on your device, even offline once the page has loaded.