For a standard 18‑pound turkey roasted in a conventional oven at 325°F (163°C), plan on about 3¾ to 4½ hours, depending mainly on whether it’s stuffed and on your specific oven.

Quick Scoop

  • Unstuffed 18 lb turkey:
    • Typical guideline: 13–15 minutes per pound at 325°F
    • Approximate total time: 3½–4½ hours until it reaches 165°F in the thickest part of the breast and thigh.
  • Stuffed 18 lb turkey:
    • Needs a bit longer in the oven at the same temperature.
    • Approximate total time: 4–4¾ hours, again confirming 165°F in both the meat and the center of the stuffing.
  • Safety first:
    • Go by internal temperature , not just the clock. The turkey is done when the breast and thigh both hit 165°F and juices run clear.
* Let it rest 20–30 minutes before carving so it stays juicy.

In practice, most home cooks start checking the temp around the 3½‑hour mark for an unstuffed bird and around 4 hours for a stuffed one, then leave it in until the thermometer says it’s ready.

TL;DR: For “how long does it take to cook an 18 pound turkey,” expect roughly 3½–4½ hours at 325°F, then use a thermometer to make the final call.

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