A 20-pound turkey should be cooked in a 325°F oven for about 4 to 5 hours. Specifically, cooking times vary slightly depending on whether the turkey is stuffed or unstuffed:

• An unstuffed 20-pound turkey typically takes about 4 to 4.5 hours to cook.
• A stuffed 20-pound turkey will take closer to 4.5 to 5 hours.

The best way to ensure the turkey is properly cooked is to use a food thermometer to check that the internal temperature reaches 165°F in the breast and 175°F in the thigh. This prevents undercooking and ensures food safety. Cover the turkey with foil if the skin starts to brown too much before the cooking time is complete to avoid burning.