Cook for 12 to 25 minutes per pound of tri-tip depending on how well-done you want the roast. When the internal temperature reaches 125 degrees F, the roast is rare. A temperature between 130 to 135 degrees F is medium rare, and a 145-degree F internal temperature denoting a well-done roast. And don’t forget, the temperature rises at least 5 degrees after you remove it from the grill or oven.