Roast Timing by Weight Calculator: Beef, Pork, Lamb and Chicken Roasting Times
Estimate oven roasting time from the weight and cut of beef, pork, lamb or a whole chicken, using the USDA roasting timetables: doneness from rare to well done, any oven temperature, the temperature to take it out at, a time range, resting time and a time-by-weight table.
How it works
Roast time = weight × USDA minutes per pound for the cut (beef and lamb at 325°F, pork at 350°F, to 145°F) × doneness and oven adjustment · Adjustment = ln[(oven − 40°F) ÷ (oven − target)] ÷ ln[(USDA oven − 40°F) ÷ (USDA oven − 145°F)] · Take out at = target − 5 to 10°F carryover
The starting point is the USDA roasting timetables, which give minutes per pound for each cut in a preheated oven with meat straight from the refrigerator: for example 23–25 min/lb for a bone-in beef rib roast and 20–25 min/lb for a bone-in leg of lamb at 325°F, and 20 min/lb for a pork loin roast at 350°F, all to an internal 145°F. A whole tenderloin is timed by its thickness (45–60 minutes at 425°F), and a whole chicken by the USDA totals for its weight at 350°F (1¼–1½ hours for 3–4 lb). The USDA charts stop at the 145°F safe minimum, so for rarer or more-done roasts, or a different oven temperature, the calculator scales the time with a simple heat-transfer estimate (Newton’s law of heating): time is proportional to ln[(oven − starting temperature) ÷ (oven − target)]. Getting the centre to 160°F takes about 19% longer than to 145°F at 325°F, and 125°F about 23% less. Large roasts keep rising 5–10°F after they leave the oven (carryover cooking), so the calculator shows the temperature to take the roast out at and a resting time. Shape, bone, fat, starting temperature and oven accuracy all change the real time, so always finish with an instant-read thermometer in the thickest part, away from bone.
Worked example
With the defaults, a 4 lb bone-in beef rib roast cooked to medium (145°F) at 325°F takes the USDA’s 23–25 min/lb: 4 × 23 = 92 minutes to 4 × 25 = 100 minutes, so about 1 h 36 min. Start checking at about 1 h 15 min (80%), take it out at about 138°F (7°F of carryover for a 4 lb roast) and rest it 15–20 minutes. For medium-rare (135°F) the time drops by the factor ln(285 ÷ 190) ÷ ln(285 ÷ 180) = 0.882 to about 1 h 25 min.
Sources: USDA FSIS: Beef from Farm to Table (roasting timetable) · USDA FSIS: Fresh Pork from Farm to Table (roasting timetable) · USDA FSIS: Lamb from Farm to Table (roasting timetable) · USDA FSIS: Chicken from Farm to Table (roasting timetable) · FoodSafety.gov: Safe minimum internal temperatures
Frequently asked questions
How long do I cook a roast per pound?
At 325°F the USDA lists 23–25 minutes per pound for a bone-in beef rib roast and 30–35 for a round or rump roast, 20–25 for a bone-in leg of lamb, and 20 minutes per pound for a pork loin at 350°F, all to 145°F. Rarer roasts need less time and well-done roasts more.
Should I go by time or temperature?
Temperature. Time is for planning, but the internal temperature at the thickest point decides doneness and safety. The USDA minimum for beef, pork and lamb roasts is 145°F with a 3-minute rest, and 165°F for chicken.
When should I take the roast out of the oven?
About 5°F before the target for small roasts and up to 10°F for large ones. Heat stored in the outer layers keeps flowing to the centre while the roast rests, so it finishes at the target.
How long should a roast rest?
At least 3 minutes by the USDA rule, but 15–20 minutes for most roasts and up to 30 for very large ones, loosely covered with foil. Resting lets the temperature even out and keeps the juices in when you carve.
Does a hotter oven cook a roast faster?
Yes, but less than you might expect, and the outside overcooks more. Going from 325°F to 350°F cuts the time by about 10% for a 145°F target. Many cooks sear at high heat first or finish with a blast of heat for browning.
Does bone-in change the timing?
Boneless rolled roasts take longer per pound than bone-in ones in the USDA charts (for beef rib, add 5–8 minutes per pound) because they are thicker and more compact. Always probe away from the bone for an accurate reading.
Related calculators
Cooking times are estimates. Check doneness with a food thermometer: 145°F with a 3-minute rest for whole cuts of beef, pork and lamb, and 165°F for poultry.