Apartment Therapy has developed a formula to determine the amount of candy to buy for Halloween. The formula taxes into account the approximate number of kids in your neighborhood, the weather, and how enthusiastic your neighborhood is about the holiday. The formula should prevent you from having any sad Elsas or Batmen at your door and if you overestimate it doesn't hurt to have leftover candy to snack on, even if it lasts you all of the way to Thanksgiving.