How the estimate works
Roasting time grows with weight, so cookbooks give a time in minutes per pound for each cut and oven temperature. This calculator multiplies the weight by a typical rate:
| Roast | Oven | Minutes per pound | Pull at (inside) |
|---|---|---|---|
| Beef rib roast, medium-rare | 325 °F | about 24 | 145 °F |
| Beef rib roast, medium | 325 °F | about 28 | 160 °F |
| Pork loin roast | 350 °F | about 20 | 145 °F |
| Whole chicken | 350 °F | about 20 | 165 °F |
| Leg of lamb, medium-rare | 325 °F | about 22 | 145 °F |
| Fully cooked ham, reheated | 325 °F | about 18 | 140 °F |
The temperatures follow USDA guidance: 145 °F with a 3-minute rest for whole cuts of beef, pork and lamb, 165 °F for poultry and 140 °F to reheat a fully cooked ham. Many cooks pull beef a few degrees earlier for a rarer center, but 145 °F is the official safe minimum.
Worked example
A 3.5 lb beef rib roast, medium-rare, at 325 °F:
- Time: 3.5 × 24 = 84 minutes, or 1.40 hours.
- Start checking with a thermometer at about 63 minutes (75% of the estimate).
- Take it out when the center reaches 145 °F.
- Rest for 15 minutes before carving, loosely covered with foil.
Why a thermometer beats the clock
Minutes per pound are a planning tool. The real time depends on:
- Shape: a long, thin roast cooks faster than a thick, round one of the same weight.
- Starting temperature: a roast straight from the fridge takes longer than one that sat out for 30 minutes.
- Bones: bone-in roasts often cook a little more slowly near the bone.
- Your oven: many ovens run 10 to 25 °F hotter or cooler than the dial.
Insert an instant-read or probe thermometer into the thickest part, away from bone and fat. For a whole chicken, check the thickest part of the thigh and the breast.
Resting and carryover cooking
When a roast leaves the oven, its outer layers are much hotter than the center, so the inside keeps warming by about 5 °F during the rest. Resting also lets the juices thicken slightly, so less runs onto the cutting board. Plan the rest into your timing: the roast stays hot for 20 to 30 minutes under foil, which gives you time to make gravy and finish side dishes.