How Long do You Cook a Pork Loin Roast?

A pork loin roast will take anywhere from 1 hour to 2 1/2 hours to cook. A small single loin (2 to 4 lbs.), enough for a small family, will need to roast at 325 degrees for 1 to 1 1/4 hours, or until the internal temperature reaches 160 degrees.