Butterball has a handy web calculator that really helps with cooking times. Most people OVERCOOK the bird. Find a good thermometer to test the temperature of the bird - it makes all the difference. I usually take mine out when thickest part of breast registers 165 degrees and thickest part of thigh registers 170 to 175 degrees on instant-read thermometer. Let the turkey rest 35 to 40 minutes before carving!
Turkey Cooking Times site: