For a 20-pound bird, you’re looking at about 4 to 4.5 hours in a 325°F oven. That’s if it’s completely thawed. Yes, I said completely—none of that “still a little icy in the middle” business.
But wait. That’s just the math part. The real answer is “until it hits 165°F in the thickest part of the thigh.” Your oven is a liar. Every oven runs hot or cold. So trust your thermometer, not the clock.
But what if the turkey is still frozen? (Please don’t do this)
Look, I know you’re in a pinch. Maybe you forgot to thaw it. (Hey, it happens to the best of us.) A frozen 20-pounder will take roughly 6 to 7 hours. That’s a long time. It’s also risky—the outside will dry out before the inside is safe.
If you absolutely must cook from frozen, use a lower temp (like 300°F) and plan on a very late dinner. And maybe have some takeout menus on standby. Just saying.