I've seen suggestions ranging from 1/2 to 3/4# per person.
Wife who over does everything food related says no way. She insists
that turkey's have too much waste for that calculation. She suggest
(insists)
that our 11 person gathering will require an 18# bird.
Don't know how she does the math, but that's her majic number.
Been married long enough to know that one must pick their battles.