Guide
Party quantity planner
Guest numbers turned into how many plates, forks, cups, candles and balloons to have in, with a margin for the ones that get dropped.
Turn a guest list into quantities
Rules of thumb, not physics. They lean deliberately towards having spare, because running out mid-event costs more than a few leftover forks.
The arithmetic most people get wrong is drinkware. Guests put a cup down, lose track of it and take a fresh one, so cup counts run well ahead of head counts at anything longer than a couple of hours. Plates and cutlery track the number of times food is served rather than the number of people in the room.