For a classic oven-roasted rib roast (prime rib), plan roughly 15–20 minutes per pound at moderate heat, but always cook to internal temperature, not time alone.

Core timing guidelines

  • For a slow roast at 225°F (about 107°C) :
    • 4 lb: about 2 hours for medium-rare.
* 5 lb: about 2.5 hours.

* 6 lb: about 3 hours.

* 7 lb: about 3.5 hours.

* 8 lb: about 4 hours.

* 10 lb: about 5 hours.
  • For a blast-then-lower method (common holiday style):
    • Start at 450–500°F (232–260°C) for 20 minutes to form a crust, then reduce to 325–350°F (163–177°C) until it reaches target temp.
* One recipe suggests a total of ~15 minutes per pound at 500°F for 20 minutes, then 325°F for the remainder.

* Another uses 20 minutes at 450°F, then about 11 minutes per pound for rare and 13 minutes per pound for medium-rare at 350°F.

Target internal temperatures

Use an instant‑read thermometer in the thickest part of the roast; this matters more than minutes.

  • Rare: pull at about 115°F (46°C) ; it will rise during rest.
  • Medium‑rare: pull at about 120–125°F (49–52°C).
  • Medium: pull at about 130°F (54°C).

Let the roast rest 20–30 minutes before carving so juices redistribute and carryover cooking finishes the center.

Simple example schedule (6–8 lb roast)

  • Bring to room temperature for 2–3 hours before cooking.
  • Preheat to 450–500°F, roast for 20 minutes.
  • Reduce to 325–350°F and continue roasting:
    • 6 lb: roughly 1–1.5 more hours for medium-rare (total around 1.5–2 hours).
* 8 lb: roughly 1.5–2 more hours (total around 2–2.5 hours).
  • Start checking internal temp early to avoid overcooking.

Quick notes and forum-style wisdom

Public cooking discussions and recipe comments often emphasize that ovens vary , so timing charts are only planning tools, not guarantees. Many home cooks say the “secret” to a perfect rib roast is:

  1. Season simply (often just salt and pepper).
  1. Use a reliable meat thermometer.
  1. Rest the meat well before slicing to keep it juicy.

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Wondering how long to cook a rib roast? Learn trusted minute‑per‑pound guidelines, oven temperatures, and internal temp targets for perfect medium‑rare prime rib, plus tips from recent recipes and forum discussions.

Information gathered from public forums or data available on the internet and portrayed here.