How Long to Roast a Leg of Lamb
A leg of lamb roasted at 325F follows a dependable minutes-per-pound rule, but the exact number depends on two things: whether the cut has the bone in and how pink you want the center. Bone-in legs cook faster because the bone conducts heat into the deepest part of the meat, while a boneless, butterflied-and-tied leg is denser and needs more time per pound. For medium-rare, plan on roughly 15 minutes per pound bone-in and about 20 minutes per pound boneless. A 6 lb bone-in leg lands near 1 hour 30 minutes, while a 5 lb boneless leg runs closer to 1 hour 40 minutes.
Roast time = weight (lb) x min/lb x fridge factor
If the lamb goes in straight from the refrigerator instead of resting on the counter for an hour, add roughly 12 percent to the clock so the cold core has time to come up to temperature.
Pull Temperature and Resting
The single most important number is the pull temperature, not the clock. Lamb keeps cooking after it leaves the oven, and carryover heat raises the internal temperature about 5F while it rests. That means you pull at 125F for a final medium-rare of 130F, or at 135F for a final medium of 140F. Always probe the thickest part of the leg, avoiding the bone.
Why Resting Is Non-Negotiable
Tent the roast loosely with foil and rest it 15 to 20 minutes before carving. Resting lets the muscle fibers relax and reabsorb juices that would otherwise spill onto the cutting board, so the slices stay moist. Skip the rest and you lose both temperature accuracy and a good measure of the juices. Slice against the grain for the most tender bite.
Frequently Asked Questions
How long do you cook a leg of lamb per pound?
At 325F, plan on about 15 minutes per pound for medium-rare bone-in lamb and about 20 minutes per pound for boneless. Adjust up for more doneness: roughly 18 min/lb bone-in for medium and 26 min/lb for well-done. The calculator builds these rates in and adds time if the lamb starts cold from the fridge.
What temperature should leg of lamb be cooked to?
Pull the lamb a few degrees early because it keeps cooking while it rests. For medium-rare, remove it at 125F so it finishes at 130F; for medium, pull at 135F for a final 140F. Insert the thermometer into the thickest part of the leg without touching the bone, which reads hotter than the meat.
Is bone-in or boneless leg of lamb better?
Bone-in legs are more forgiving and develop deeper flavor, and the bone speeds cooking by conducting heat to the center. Boneless legs are easier to carve and can be stuffed or butterflied, but they are denser and need more minutes per pound. Either works well with this calculator once you select the cut.
Do I need to rest the lamb before carving?
Yes. Tent it loosely with foil and rest a boneless leg about 15 minutes and a bone-in leg about 20 minutes. Resting lets the juices redistribute so they stay in the meat instead of running out, and carryover heat brings the center to its final target temperature during this window.
Practical Guide for Leg of Lamb Cooking Time Calculator
Work backward from when you want to serve. The calculator adds your roast time and a 15 to 20 minute rest, then tells you the latest moment to slide the lamb into a preheated 325F oven so it is sliced and on the table at your serve time. Build in a 15 minute cushion, because oven recovery after opening the door and a slightly cold core can stretch the clock.
Treat minutes per pound as a planning estimate and let the thermometer make the final call. Oven calibration, the shape of the leg, and how long the meat sat out all shift the real cook time. A leave-in probe set to alert at your pull temperature removes the guesswork: when it beeps at 125F for medium-rare, the lamb is ready regardless of what the clock says.
Let the lamb come toward room temperature for about an hour before roasting whenever you can. A leg that goes in cold from the fridge has a chilled center that drags the cook time out and can leave the outer band overdone before the middle catches up. If you are short on time, pick the from-the-fridge option so the calculator adds the extra minutes that cold core demands.
Quick Checklist
- Roast at 325F and select bone-in or boneless so the per-pound rate is right.
- Pull medium-rare at 125F (130F final) or medium at 135F (140F final).
- Probe the thickest part of the leg, keeping the tip away from the bone.
- Rest tented in foil 15 to 20 minutes, then carve against the grain.