How Long Does It Take to Cook Lamb?
The length of time it takes to cook lamb depends on the cut of the meat and how much that cut weighs; for example, a 5- to 7-pound bone-in leg of lamb roasted at 325 degrees Fahrenheit to medium rare, or 145 F, takes between an hour and 40 minutes to slightly less than 3 hours. In general, lamb should cook for between 15 to 50 minutes per pound; the thicker the cut, the longer the cooking time.
Lamb is considered to be done to a medium temperature when cooked to 160 F, while well done lamb reaches a temperature of 170 F. Rolled boneless leg of lamb takes between an hour and 40 minutes and 4 1/2 hours for a 4- to 7-pound cut. Rib or loin chops that are 1 to 1 1/2 inches thick take from 7 to 12 minutes cooked to medium rare when grilling.