How Long to Cook Prime Rib?

Timing by doneness (per pound, at 325°F)

Why an internal thermometer matters more than the clock: prime rib roasts vary in shape and bone content, so time-per-pound is only a starting estimate — always finish based on a meat thermometer inserted into the thickest part, not the clock alone.

Resting is not optional. After removing from the oven, tent loosely with foil and rest for 20–30 minutes. The internal temperature will climb another 5–10 degrees during this time, and skipping it causes the juices to run out when carved rather than staying in the meat.

Two other methods worth knowing

• Reverse sear: cook low and slow (225–250°F) until close to the target temperature, then finish with a very hot, short blast (500°F+ for 10–15 minutes) to brown the crust. Gives the most even doneness edge to edge.
• Low and slow with a hot finish (a variant of the above): similar idea, roast at a low temperature for most of the cook, then raise the oven heat only at the end for browning.

A quick reference for a typical roast: a common 5-pound prime rib at 325°F for medium-rare takes roughly 1 hour 15 minutes to 1 hour 40 minutes, plus the 20–30 minute rest.

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