Prime Rib Cooking Time Calculator
Estimate roasting time for prime rib.
~15 (medium-rare, 325°F)
Results update as you type.
How it works
Prime rib is a special-occasion roast where timing matters, and this calculator estimates how long to cook it. You enter the roast's weight and the minutes per pound for your desired doneness, and it returns the total roasting time in minutes and hours. A common guideline for prime rib at 325°F is about 15 minutes per pound for medium-rare, a little less for rare and more for medium and beyond, so a 6-pound roast takes roughly 90 minutes. However, cooking time is only a starting estimate — the reliable way to nail doneness is an instant-read or leave-in meat thermometer, since roast shape, bone, starting temperature, and oven accuracy all affect timing. Pull the roast when its internal temperature is about 5 to 10 degrees below your target, because it continues cooking while resting; medium-rare is around 130 to 135°F final. Always rest the roast for 15 to 20 minutes before carving so the juices redistribute. Some cooks use a high-heat sear followed by low roasting, or the reverse-sear method, which changes timing, so treat this estimate as a plan and let the thermometer make the final call. Enter the weight and minutes per pound to estimate the roasting time.
Roasting time = weight × minutes per pound
The estimated roasting time equals the roast's weight multiplied by the minutes per pound for your target doneness and oven temperature. Prime rib is commonly figured at about 15 minutes per pound for medium-rare at 325°F, but a meat thermometer is the true guide to doneness.
Source:Roasting guidelines
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter roast weight.
- 2
Adjust the options
Adjust minutes per pound if they apply — sensible defaults are already set.
- 3
Read your result
Total roasting time updates instantly as you type — no button to press.
Frequently asked questions
How long do you cook prime rib per pound?
A common guideline is about 15 minutes per pound at 325°F for medium-rare, slightly less for rare and more for medium. So a 6-pound roast takes roughly 90 minutes. This is only an estimate, though — a meat thermometer is the reliable way to reach your target doneness, since many factors affect actual cooking time.
What internal temperature should prime rib reach?
For medium-rare, aim for a final internal temperature around 130 to 135°F; rare is about 120 to 125°F and medium about 140 to 145°F. Because the roast keeps cooking while resting, pull it 5 to 10 degrees below your target. Always use a meat thermometer rather than relying solely on time for a perfect result.
Why should I use a meat thermometer?
Cooking time is only an estimate because roast shape, thickness, bone, starting temperature, and oven accuracy all affect how fast the meat cooks. A thermometer measures the actual internal temperature, the true indicator of doneness, letting you avoid overcooking an expensive roast. Insert it into the thickest part, away from bone, for the most accurate reading.
Do I need to rest prime rib after cooking?
Yes, always rest it 15 to 20 minutes before carving, loosely tented with foil. Resting lets the juices, driven to the center by heat, redistribute throughout the meat, so they stay in the roast instead of spilling out when you cut. The internal temperature also rises several degrees during this rest, completing the cooking.
Does bone-in prime rib change the cooking time?
Somewhat. Bone-in roasts can cook a little more slowly and unevenly than boneless because the bone affects heat conduction, and the bone also adds weight that is not meat. Many cooks find bone-in delivers great flavor and moisture. Regardless, rely on a thermometer inserted into the meat away from the bone to judge doneness accurately.