Prime rib cook time calculator
Prime rib is the most expensive thing most people ever cook, usually on the one day of the year when getting it wrong is least forgivable. Enter the weight and your temperature for a cook range, a pull temperature that accounts for carryover, and the hour to put it in.
Local conditions
Off by default. Turning it on asks your browser where you are, or you can type a town instead. Nothing is requested until you do. Altitude then adjusts the cook time using the USDA figure; weather is described but never changes a number.
These are estimates. Cook to internal temperature, not to the clock — two cuts of identical weight can finish hours apart. USDA FSIS lists beef roasts at 145F with a 3-minute rest. A prime rib cooked to medium rare sits below that, which is a personal risk choice on whole-muscle beef, not a USDA-safe one.
Cooking something else? The full smoking calculator covers every cut, including chicken, turkey, chuck roast, pork loin, beef short ribs and salmon.
How it works
Roughly 35 to 45 minutes per pound at 225F. A standing rib roast is graded by ribs as well as weight: budget about two pounds per rib, so a four-bone roast is around 8 lb and a six to eight hour affair at low temperature.
Pull temperature is lower here than on any other cut on the site, and that is deliberate. A large dense roast carries over five to ten degrees while it rests, against three to five on a small cut, so pulling at 125 to 130F is what actually lands you at medium rare. Pull at 135F and you will serve medium well.
There is no stall. Prime rib has little connective tissue and is cooked to doneness rather than to tenderness, so the internal temperature rises steadily and predictably from start to finish.
This is a reverse sear by default: low heat until it is nearly there, a rest, then a short blast at high heat for the crust. The 20 to 30 minute rest in the output is the low-heat rest, before any searing.
What it assumes
- Bone-in standing rib roast, going in cold from the fridge. Boneless cooks slightly faster and loses the rib bones' insulating effect on the underside.
- Medium rare is the target. USDA FSIS lists beef roasts at 145F with a three-minute rest, which is well past medium rare. Cooking a whole-muscle roast to 130 to 135F final is a personal risk choice, and the standard one for this cut.
- Carryover is included in the pull temperature, not added afterwards. Do not subtract it twice.
- Height above sea level changes nothing here. A standing rib roast is dry heat with no evaporative plateau, and USDA's own guidance is to use sea-level times when oven-roasting. The local conditions panel will still show your elevation, and still show an adjustment of none.
Questions
About 35 to 45 minutes per pound at 225F. At 250F it moves closer to 30 to 35. Higher than that and you trade the even edge-to-edge interior that low temperature buys you.