Calculate the appropriate turkey size by allocating 1 to 1 1/2 pounds of turkey for each person participating in the meal. For example, a turkey weighing 8 to 12 pounds is suitable for a party of eight people.
A turkey that works out to 1 pound per person is sufficient for moderate appetites if you do not want leftovers, while 1 1/2 pounds per person is generally a good estimation for a mix of appetites if you want leftovers.
A calculator on the Butterball website suggests purchasing 1/2 pound of turkey for each child, 1 pound of turkey for each adult who is a light eater and 1 1/2 pounds of turkey for each adult who is a big eater. It also suggests adding 1/2 pound of turkey per adult on top of these calculations to provide enough for leftovers.