The short answer: for a typical dinner, plan on roughly 6-8oz of cooked protein, 4-6oz of a starch or side, 2-3oz of salad, 1-2 pieces of bread, and one dessert portion per adult guest. But the real answer depends on your service style, meal type, and guest list - which is exactly what this guide (and the calculator below) walk through.
Protein: 6-8oz for dinner, 4-6oz for lunch, less for a lighter breakfast protein
Starch / side: 4-6oz per person, regardless of meal
Salad: 2-3oz per person
Bread: 1-2 pieces per person
Dessert: One portion per person, sized to the dessert style
A buffet runs a bit higher than plated portions - guests serve themselves, and there's some natural overage built into that. Family-style lands close to buffet. Cocktail or passed-apps events are the outlier: guests sample smaller amounts across many more items, so per-category quantities drop noticeably even though the total number of bites someone eats stays similar.
Caterers typically build in a safety buffer on top of raw portion math - commonly around 15% for events under 200 guests. For larger events, that percentage can shrink a bit (closer to 10-11%) since individual appetite variance averages out more across a bigger crowd. Kids on the guest list also matter: they typically eat around half an adult portion, though every family is different.
Rules of thumb get you close, but the real math - service style multiplier, meal-type base portions, buffer scaling, and how many kids are coming - adds up fast by hand. That's exactly what the free calculator below does automatically for your specific guest count.
Plug in your guest count and get exact numbers in seconds.