A typical pork sirloin roast that weighs between 2 and 5 pounds takes between 20 and 30 minutes per pound to cook completely. Bone-in pork sirloin roasts cook at a slightly faster rate than boneless roasts.
A pork sirloin roast should cook until the roast reaches an internal temperature of 145 degrees when cooked at 325 F. The pork roast is juicy with just a hint of pink in the middle. Cooking whole cuts of pork like a roast past this temperature is fine, but can cause the meat to dry out. It is also important to allow the pork roast to rest at least 3 minutes after removing it from the oven.