Because the turkey takes up considerably more space in the oven when spatchcocked, it's best to try to limit this process to turkeys under 20 pounds. It really depends on your particular oven space and your pans. I've found that spatchcocking works beautifully for 12 to 15 pound turkeys, and they fit beautifully on half sheet baking sheets. However, I've also spatchcocked a 25-pound turkey and placed it on an extra large roasting pan.