How this calculator works
A whole turkey roasts at 325 F (163 C) and the time per pound falls as the bird grows, because a large bird has less surface area for its mass and loses less heat. The USDA timetable gives a range for each weight band: start checking at the early end, because ovens vary, a stuffed bird takes longer, and a bird that has been in the fridge is colder at the centre. Stuffing is the part that changes the time most, and it is also the part with the greatest safety risk: the stuffing must reach 74 C (165 F) as well as the meat. The only reliable test is a thermometer in the thickest part of the thigh and in the stuffing, and the target for a whole bird is higher than for pieces.
Formula
find the weight band that contains the turkey weight in pounds, then take the lower and upper hours for stuffed or unstuffed. Weight in pounds = kilograms / 0.45359237. The range is the USDA timetable at 325 F for a whole bird, from 2.75 to 3 hours at 8 to 12 lb up to 4.5 to 5 hours at 20 to 24 lb. Rest for 20 minutes.
Worked example
A 6 kg turkey is 6 / 0.45359237 = 13.2 lb, which is in the 12 to 14 lb band. Unstuffed, the range is 3 to 3.75 hours, so start checking at 3 hours. Stuffed, the range is 3.5 to 4 hours. The bird is done at 82 C (180 F) in the thigh under the Health Canada chart, or 74 C (165 F) under the USDA guidance, and the stuffing must reach 74 C in both.
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Frequently asked questions
Should I stuff the turkey?
Stuffing lengthens the cooking time and creates a separate food safety check, because the stuffing must reach 74 C (165 F) and it sits in the coldest part of the bird. Many cooks bake the stuffing separately for that reason. If you do stuff the bird, pack it loosely and check its temperature as well as the meat.
What internal temperature should turkey reach?
Health Canada lists 82 C (180 F) for a whole bird and 74 C (165 F) for pieces and ground poultry. The USDA lists 165 F (74 C) for the thigh, breast and stuffing. Measuring in the thigh, away from the bone, is the reliable place; the breast can read higher while the thigh is still under.
Why is the oven temperature fixed at 325 F?
The USDA timetable is based on 325 F, and roasting at a higher heat browns the outside before the centre is safely cooked, while a lower heat makes the timing unreliable. If you cook at another temperature, use a tested recipe for that temperature and rely on the thermometer.
Can I cook a turkey from frozen?
It is possible in some ovens and appliances, but it takes much longer and the outside can overcook before the centre is safe. The USDA timetable here assumes a thawed bird. Thawing in the fridge takes about 24 hours for every 4 to 5 pounds, so a 20 lb bird needs several days.