Work out buffet quantities and cost per person.
Buffet quantities are driven by self-service behaviour rather than appetite. Caterers plan on roughly 180 g of main protein and 250-280 g of sides per adult, then add about fifteen percent on top, because early guests serve themselves generously and a platter that looks depleted stops being taken from — presentation volume is part of the requirement, not waste. Multiplying total weight by an average cost per kilogram gives the food budget, and dividing back by guest count gives the per-head figure that makes a buffet comparable with a plated meal. Buffets usually win on cost per head precisely because the sides, which are cheap per kilogram, carry more of the volume.
Buffet quantities and cost per head
Main kg = main grams x guests x 1.15 / 1000; sides kg = sides grams x guests x 1.15 / 1000; total cost = (main kg + sides kg) x cost per kg; cost per guest = total cost / guests
Because a buffet needs to look full to keep being used, and the first third of guests take larger portions than the last. Without the margin the final guests get a picked-over table, which is the most common complaint about self-service catering.
Count them as about half an adult for protein and two-thirds for sides. Teenagers, however, should be counted as more than one adult if the main is popular.
Buffets are normally cheaper per head because sides carry the volume and service labour is lower, but they need more total food. A plated meal wastes less and portions predictably, which is why formal events prefer it despite the cost.