Believe it or not, basic algebra will get you a moist, beautifully burnished bird. All it takes is a simple equation. Start by identifying the most important variable — the number of guests. This will determine the size of the turkey you’ll need. Use this information to estimate the thawing and roasting times (plus or minus 10 minutes). Hate math? Don’t worry — Real Simple has done the calculations for you.

Number of Diners: 8.
Turkey Size (including leftovers): 10 to 12 pounds.
Thawing Time (for a frozen turkey): Refrigerator, 2 to 2 1/2 days; cool water (changed every half hour), 5 to 6 hours.
Roasting Time (unstuffed): Roast at 425° F for 45 minutes. Cover with foil, reduce temperature to 350° F, and continue to roast until a thigh registers 180° F, about 2 hours total .

Number of Diners: 12.
Turkey Size (including leftovers): 16 to 18 pounds.
Thawing Time (for a frozen turkey): Refrigerator, 3 1/2 to 4 days; cool water (changed every half hour), 8 to 9 hours.
Roasting Time (unstuffed): Roast at 425° F for 45 minutes. Cover with foil, reduce temperature to 350° F, and continue to roast until a thigh registers 180° F, 2 1/2 to 3 hours total.

Number of Diners: 16.
Turkey Size (including leftovers): 20 to 22 pounds.
Thawing Time (for a frozen turkey): Refrigerator, 4 to 4 1/2 days; cool water (changed every half hour), 9 to 11 hours.
Roasting Time (unstuffed): Roast at 425° F for 45 minutes. Cover with foil, reduce temperature to 350° F, and continue to roast until a thigh registers 180° F, 3 to 3 1/2 hours total.

Number of Diners: 20.
Turkey Size (including leftovers): 24 to 26 pounds.
Thawing Time (for a frozen turkey): Refrigerator, 5 to 5 1/2 days; cool water (changed every half hour), 11 to 13 hours.
Roasting Time (unstuffed): Roast at 425° F for 45 minutes. Cover with foil, reduce temperature to 350° F, and continue to roast until a thigh registers 180° F, 4 to 4 1/2 hours total.

Talking Turkey

Call either of these hotlines to speak with an expert turkey roaster, pie baker, or side-dish maker. Hours listed are for Thanksgiving Day.

Butterball Turkey Talk-Line: 800-288-8372, 6 a.m. to 6 p.m. eastern standard time; www.butterball.com.

U.S. Department of Agriculture Meat and Poultry Hotline: 888-674-6854, 8 a.m. to 2 p.m. eastern standard time; www.fsis.usda.gov.

Tip: Roast two small turkeys side by side rather than one extra-large bird. They’ll be done in almost half the time.