Many caterers or food industry companies, such as Chefs-Menus.com or PlanningHelper.com, offer charts or calculators on their websites that provide information as to how much food to prepare based on the number of people expected to consume the meal. These calculations are based on how much of a particular food an individually typically eats.
Catering companies estimate their total fees based on a specific menu, taking into consideration the proportions likely consumed by an attendee, as well as the cost of the ingredients and the time it takes to prepare the menu.
As the number of food options or dinner courses grows, the portions for an individual often decreases. This might not apply with items such as certain cuts of meat or desserts.
It is important to consider your audience when planning a menu as certain groups might be inclined to consume one type of food more than another.
There are a number of variables to consider, including the time that lapses between appetizers and dinner, a factor which might influence how many hors d’oeuvres to prepare. It's also important to consider how much how many courses will be served as well as how filling certain foods might be. In a similar fashion, the volume of beverages needed will increase the longer the event.