Roast Cooking Time Calculator

The one rule that matters: cook to temperature

Every roast on this page is different — a bone-in prime rib behaves nothing like a boneless pork loin, and a rolled leg of lamb cooks in half the time of the same weight bone-in. What they share is that they are all done when they hit a specific internal temperature, and no minute-per-pound table is a substitute for a probe thermometer in the thickest part of the meat. The estimates above will get your roast into the oven at roughly the right moment; the thermometer is what tells you when it comes back out.

Safe internal temperatures at a glance

• Beef, pork, and lamb (whole-muscle): USDA minimum 145°F with a 3-minute rest. Rare (125°F) and medium-rare (135°F) beef and lamb are widely eaten but are below the USDA recommendation.
• Ground beef, pork, or lamb: 160°F, no rest.
• Poultry (whole or parts): 165°F in the thickest part of the thigh, not touching bone.
• Fully-cooked ham: 140°F (reheat only).
• Fresh (uncooked) ham: 145°F with a 3-minute rest.

Why the estimates are ranges

Two identical-looking roasts can finish 30 minutes apart because of things you can't see. Fridge-cold meat takes longer than meat that's been tempered on the counter for 45 minutes. Bone-in cuts conduct heat differently to boneless. A dark enamel roasting pan absorbs radiant heat and pushes the outside faster than a shiny aluminium one. Home ovens routinely swing 25°F above and below their set temperature, and convection fans (if you use them) shave another 10–15%. The range above is wide enough to cover most of that variation; the thermometer closes the last gap.

Carry-over cooking is real — pull the roast early

Once you pull a roast out of a 325°F oven, its internal temperature keeps climbing for another 10–15 minutes as heat from the outside migrates inward. For a mid-size roast that's about 5°F; for a large prime rib it can be closer to 10°F. If you're aiming for 135°F medium-rare, pull the roast at 128–130°F and let carry-over do the rest. Cooking straight to 135°F in the oven usually lands you at medium (145°F) by the time you slice.

Why resting matters

A hot roast sliced immediately loses juice everywhere — you can watch it pool on the board. During roasting, muscle fibres contract and squeeze moisture toward the centre; a 15–20 minute rest under a foil tent lets the fibres relax and the juices redistribute so they end up on the meat instead of the counter. Rest longer for larger cuts: a 12-pound prime rib benefits from 30 minutes.

Ham is different — most hams are already cooked

Nearly every ham in a supermarket is labelled "fully cooked" and only needs to be reheated to 140°F, not cooked to a doneness temperature. That's why the ham estimates above are shorter — you're warming a cooked product, not roasting a raw one. A fresh (uncooked) ham is a different animal: treat it like a pork roast and take it to 145°F with a 3-minute rest.

Whole chicken cooks hot and fast

Chicken benefits from a hotter oven (375–425°F) to crisp the skin without overcooking the breast. The table above uses 375°F as a middle ground. Spatchcocked (butterflied) chickens cook faster and more evenly than whole birds — expect 45 minutes total for a 4-pound spatchcocked bird at 425°F.