A boneless pork loin roasts in a 350 degrees Fahrenheit oven for 20 to 25 minutes per pound or until the internal temperature of the roast reaches between 145 degrees and 160 degrees Fahrenheit on a meat thermometer. A bone-in roast requires a slightly longer cooking time.
When roasting pork, the optimum cooking time is based on size of the roast and whether or not the bone is present. When the roast has a bone, additional cooking time of 5 to 10 minutes per pound is required for the roast to reach the proper internal temperature. The oven temperature does not change based on the size of the pork loin.