Hors d'oeuvres are little snack foods, small 1 or 2 bite items of food served before or outside of ("hors") the main dishes of a meal (the "oeuvres") which are intended to stimulate the appetite. The terms hors d'oeuvres and appetizers are often used interchangeably, but there is a difference: hors d'oeuvres are the small savory bites, typically finger food, served before a meal, while appetizers appear as the first course served at the table. The name hors d'oeuvres comes from the French and is literally translated as "out of the work," but it's more logical to think of it as meaning "apart from (or before) the meal."
How many hors d'oeuvres should be provided per person?
The number of hors d'oeuvres you need often depends on how long the cocktail "hour" is, the time of day, and if a meal will also be served following the cocktail hour.
For a two hour party plan for:
When hors d'oeuvres are served before a meal, plan for:
5-7 bites when served before a light meal
3-4 bites when served before a full dinner meal
People eat more during the first 90 minutes. After two hours consumption picks up again, especially if hors d'oeuvres replace dinner.
Young people eat more than an older crowd and guests eat more at casual parties than formal functions.
How many varieties should be served for an hors d'oeuvre only party?
For up to 35 guests plan for 4-5 different kinds of hors d'oeuvres
For 35-60 guests, plan for 7-9 different kinds of hors d'oeuvres
For more than 60 guests, plan for 9 or more different kinds of hors d'oeuvres
If hors d'oeuvres take the place of dinner, include some substantial meal type foods that can be served like hors d'oeuvres (for example a carving station).
Remember to provide a variety of foods to please everyone. That means something for the vegetarian as well as the meat eater. Having both hot and cold foods also helps to keep everyone nibbling happily.
If hors d'oeuvres take the place of dinner, also include several bites of sweets per person.
How do you figure how many of each type of hors d'oeuvres to prepare?
A fairly standard formula is used by caterers to figure out how many pieces should be prepared for each kind of hors d'oeuvres being served:
Number of bites desired per person times the number of guests divided by the number of different hors d'oeuvres being served.
Should hors d'oeuvres be served for breakfast or lunch?
Hors d'oeuvres are not needed for breakfast or brunch. However, 2-4 light hors d'oeuvres can be served per person for lunch, if desired.
original source: http://www.atasteful-affair.com/resources/partyplanning.html