Same ol’ story? You bought too many pizzas for your meetup? Me too. To tackle the problem, I tracked actual attendance and consumptions records across 5 meetup groups for about a year, then turned the two observed trend lines into a reusable equation.
$attendees = $rsvps > 10 ? (.8*($rsvps-10))+10 : $rsvps;
$pizzas = $rsvps > 10 ? ($rsvps/(20/3))+1.5 : $rsvps/(10/3);
Research disclaimer: This is tracked from data in non-ticketed (free) meetup events, on work nights at around 6:30pm, with adults and reasonable weather. While it may ballpark your kid’s birthday party, it isn’t adjusted for the appetites of teenagers, toddlers, or lunch. Math accounts for larger crowds tending to eat less per person and for smaller crowds to have higher attendance percentages. Read more about all of this on my blog.