Question: How Much Turkey Should I Buy?
Answer: The general rule of thumb is that you need to buy one pound of turkey for each average appetite adult. Once cooked and carved you are going to be presenting your guest with a little under 1/2 pound of turkey. This means a 20 pound turkey should feed twenty average adults.
You should adjust this size based on whether you want leftovers, how many children will be eating (plan on 1/2 pound for children) and whether or not you actually know any average adults. Remember that the larger the bird the longer the cooking time and more potential waste. You're best bet is to get close to the right size, but never under buy.