After the first 15 minutes of browning the roast in a hot oven, a rough estimate is to keep cooking it for approximately 25 minutes per pound. But this is just an estimate. As with all roasts, including ribeye roast and beef tenderloin roast, it's important to use a meat thermometer that you insert into the roast and alerts you when it's fully cooked. There's no other reliable way to ensure the roast is done. This is especially important with pork because the lowest internal temperature you want it to reach is 145 degrees (medium). I usually get a 3-pound pork shoulder. If your roast is bigger, increase the cooking time accordingly. If the top seems to be getting too dark, loosely cover it with foil.