Plan about 6 oz of cooked main, 4 oz of each of three sides, 1½ rolls and a generous dessert serving per adult, and half of that per child. Drinks: two in the first hour and one an hour after that, plus one alcoholic drink per drinking adult per hour. A pound of ice per person. Round everything up — and get the headcount right first, because that is where most over-buying comes from.
For 20 adults at a four-hour buffet dinner: 9 lb of cooked main, 6 lb of each side, 30 rolls, 30 dessert servings, 100 soft drinks, 20 lb of ice. For 30: 13½ lb of main, 9 lb of each side, 45 rolls, 45 desserts, 150 soft drinks, 30 lb of ice. For 50: 22½ lb of main, 15 lb of each side, 75 rolls, 75 desserts, 250 soft drinks, 50 lb of ice.
Those figures include the 20% extra a buffet eats compared with a plated meal. Kids change the total more than people expect: ten kids among your thirty means five fewer adult portions.
Appetizer parties are counted in bites, not ounces: 12 per adult when the appetizers are the meal, 6 when dinner follows. Offer four kinds for a small party, six for twenty to forty people, eight beyond that.
Cookouts: 1½ burgers or hot dogs per adult, one per child, one bun per each, and two sides at 4 oz per person. Watermelon feeds eight per melon.
A party planned for “about thirty” is usually twenty-two once maybes fall away, and then thirty-four when two families bring cousins. The fix is to ask for the number rather than guess it: one RSVP link that counts adults, kids and plus-ones gives you a total you can shop from, and a potluck list takes half the dishes off your list altogether.
Free · adults, kids and hours in — shopping list out
About 6 oz of cooked main, 4 oz of each side, 1½ rolls and a dessert serving per adult for a full meal; half that per child. Twelve appetizer bites per adult if there is no meal.
Two in the first hour and one an hour after that, for everyone. Add one alcoholic drink per drinking adult per hour on top.
The per-person rules above already round up. Running out is what people remember; a day of leftovers is not. Fix the headcount first and you will not need a further margin.