If attempting to estimate how many bites per person or the number of crudités trays you will need to keep your guests happy causes you a great deal of stress consider a “per-hour” option for your reception.
In the “per-hour” scenario the caterer will keep you and your guests in hors d’oeuvres for a predetermined period (typically two hours) for a fixed rate per person.
Although the rate is fixed, you will need to estimate for budget purposes how many people will attend.
And while there is no need to count canapés or skewers you should be prepared to count number of attendees as your caterer certainly will be counting heads (to see if more, not less, showed up.) And once the event is over you bill will be based on their actual number.
You can expect higher pricing per unit as the caterer must account for the worst-case scenario in planning for food (i.e. the party goer who consumes 20 bites instead of the average 4-8 bites), many event organizers find the ease of not having to concentrate on how many trays of coconut shrimp has been consumed is more than a fair trade-off.