A good rule to follow is 13 minutes for every pound of meat if there is no stuffing, and 15 minutes per pound if you are going to be stuffing your turkey. The turkey is done when it registers 165°F (74°C) in the breast part and the thickest part of the thighs reaches 170-175°F (77°C - 80°C).  A lot of people overlook this but make sure the stuffing also registers an internal temperature of 165°F (74°C).