For a 21 lb turkey, plan on about 4.5 to 5.5 hours at 325°F (163°C), depending on whether it’s stuffed and how accurate your oven is. Always rely on a meat thermometer rather than time alone: the breast should reach 165°F (74°C) and the thigh about 175°F (79°C) before you consider it done.

Quick Scoop

For a standard oven-roasted 21 lb turkey:

  • At 325°F (163°C), expect:
    • Unstuffed: roughly 4.5–5 hours.
* Stuffed: roughly 5–5.5 hours.
  • At 350°F (177°C), the time shortens slightly:
    • Unstuffed: about 4–4.75 hours.
* Stuffed: about 4.5–5.25 hours.

These ranges assume a fully thawed bird, a reasonably calibrated oven, and the turkey on the middle rack in a regular roasting pan.

Safety First: Temps, Not Just Time

The most important rule: use cooking time as a guide , but use temperature for the final decision.

  • Insert an oven-safe thermometer into:
    • The thickest part of the breast, not touching bone (goal: 165°F / 74°C).
* The innermost part of the thigh (goal: about 175°F / 79°C).
  • If stuffed, check the very center of the stuffing; it also needs to reach 165°F (74°C) for safety.
  • Once it hits temp, tent loosely with foil and rest 30–60 minutes before carving so the juices redistribute and the meat stays moist.

Factors That Change the Time

Several details can nudge your cooking time up or down for that 21 lb bird.

  • Starting temperature:
    • A turkey that’s still very cold from the fridge can add 30–45 minutes to the cook.
  • Oven accuracy:
    • Many home ovens run 25°F or more off their set temperature, which can easily shift the total cooking time.
  • Stuffed vs unstuffed:
    • Stuffed birds take longer, because the heat must penetrate the cavity and bring the stuffing to a safe temperature.
  • Pan and rack:
    • Dark roasting pans cook a bit faster than shiny ones; crowding the oven or covering tightly can slow browning and extend time.

Simple Step‑By‑Step Timeline

Here’s an easy, practical plan for roasting a 21 lb turkey at 325°F.

  1. 1 hour before roasting:
    • Take the turkey out of the fridge so it’s not ice-cold.
    • Pat it dry and season under and over the skin with salt, pepper, and fat (butter or oil).
  1. Start roasting:
    • Place on middle rack at 325°F, breast up, in a roasting pan with a rack.
    • If you like, you can start hotter (around 425°F for 45–60 minutes) for deeper browning, then drop to 325°F for the remaining time.
  1. Around 4 hours in:
    • Begin checking internal temperature every 20–30 minutes.
    • When breast hits 160–162°F and thigh is nearing 170°F, you’re close; carryover heat will finish the cook during resting.
  1. Rest:
    • Tent loosely with foil and rest 45–60 minutes before carving for a large bird like 21 lb.

If you’re planning a holiday meal, count backward from your desired serving time, adding: thawing days (if frozen) + 1 hour pre-roast prep + 4.5–5.5 hours roasting + 45–60 minutes resting.

TL;DR: For “how long to cook a 21 lb turkey,” use 4.5–5 hours (unstuffed) or 5–5.5 hours (stuffed) at 325°F as your baseline, but always confirm doneness with a thermometer at 165°F in the breast and stuffing and about 175°F in the thigh.

Information gathered from public forums or data available on the internet and portrayed here.