How this is calculated
Every dish carries a per-person quantity for one adult eating it as the only option of its
kind. Four things then move that number.
Who is eating
Adults are the unit. Teenagers count as 1.15 adults on mains and 1.3 on desserts and
drinks, because they do. Children count as half an adult on mains, six-tenths on sides and
slightly more than an adult on dessert. The headcount that matters is not the guest list,
it is the weighted appetite.
How many dishes you picked
This is the part most guides skip, and it is where over-catering comes from. People take
some of everything rather than a full portion of one thing. With two mains you need about
75% of a full portion of each rather than 100%; with three, about two thirds. Total food
still rises with variety — just far less than proportionally. Sides spread a little wider
than mains, appetizers wider still, and non-food items like plates and ice do not spread at
all.
Service style and time of day
A buffet is the baseline. Plated service cuts main-course volume by about 15% because the
portion is decided in the kitchen rather than at the table. Heavy appetizers roughly invert
the ratio — appetizer quantities go up by 80% and mains fall to 40%. A mid-afternoon event
needs about three quarters of the main course a dinner does, and rather more to pick at.
Dietary restrictions
Vegetarian and vegan guests come off the meat dishes entirely, gluten-free guests come off
anything with wheat in it, and vegan guests also come off dishes made with dairy or egg.
The reduction is proportional to the headcount affected. Vegetarian mains are then scaled
up, because the guests who cannot eat the brisket do not eat less — they eat more
of the one thing they can.
Duration
Appetizers, soft drinks and cups scale with the length of the event. Mains and sides
largely do not — people eat one meal however long they stay. Alcohol follows the standard
hosting rule of one drink in the first hour and half a drink per hour after. Ice is
budgeted at 1.5 lb per person for a four-hour event and scales from there.
Worked example. Forty guests — 24 adults, 6 teenagers, 10 children — for four
hours at a dinner-time buffet, with brisket as the only main and a 10% leftover buffer.
Weighted main-course appetite: 24 + (6 × 1.15) + (10 × 0.5) = 35.9 adult
equivalents. Three vegetarians and one vegan come off the brisket, so 36 of 40 heads
still eat it: 35.9 × 0.9 = 32.3. One main means no sharing discount. At half a pound of
raw brisket each that is 16.2 lb, and the 10% buffer takes it to 17.8 lb —
call it 18 lb, or a whole packer cut and a bit.
Ice at 1.5 lb per head for four hours: 40 × 1.5 × 1.1 = 66 lb, which is four
20 lb bags. That single line is the one hosts get wrong most often.
What this does not account for
- Your specific guests. A crowd of twenty-somethings after a hike and a crowd of
grandparents at a christening are not the same room. Use the buffer slider.
- Cooking yield. Quantities for meat are raw weights, which is how you buy them.
Brisket and pork shoulder lose 40–50% in the cook; chicken loses about 25%.
- Prices. They are rough 2026 US supermarket figures and they go stale fast. Treat
the total as a planning estimate, never a quote, and use the price level control to shift
the whole thing.
- Pack overage. The cost line is based on the quantity you need, not on what you
end up buying when a 4 lb pack is the smallest available.
- Weather. Hot days push drinks and ice up sharply and mains down.
- Allergies beyond gluten. Nut, shellfish and dairy allergies need a conversation,
not a calculator.
- Equipment. Nothing here checks whether your oven, fridge or grill can physically
handle the menu you ticked.
Common questions
How much brisket per person?
Half a pound of raw brisket per adult when it is the only main — it loses roughly half
its weight in the cook, so that lands at about four ounces on the plate. With a second
main alongside it, six ounces raw each is plenty.
How much ice do I actually need?
About 1.5 lb per person for four hours, and more if you are chilling drinks in tubs
rather than a fridge, or if it is hot. It is the most commonly underestimated item on any
party list, it is the cheapest thing you will buy, and running out of it ruins the drinks
table.
Why does picking more dishes not multiply the food?
Because appetite is roughly fixed and variety splits it. Someone at a buffet with three
mains takes a bit of each, not three dinners. Total food goes up because people take a
little more when there is more choice, but nothing like proportionally.
How much alcohol should I buy?
One drink per drinking adult in the first hour and half a drink per hour after that. Over
four hours that is about two and a half drinks each. Beer runs at roughly half of what
gets drunk, wine about a third, spirits the rest — adjust if you know the room.
Do teenagers really eat more than adults?
On mains and desserts, frequently yes. The model uses 1.15 adults on mains and 1.3 on
dessert and soft drinks, which is conservative for a room full of sixteen-year-old boys
and about right for everyone else.
What buffer should I use?
Ten per cent for a normal event. Zero only if you are cooking to a tight budget and are
genuinely happy for food to run out. Twenty-five per cent is a decision to send people
home with containers, which for a family event is often the point.
Can I trust the cost estimate?
As a planning figure, yes. As a promise, no. Grocery prices vary by region, by chain and
by month, and the numbers behind this are a snapshot. The relative shape — how much of
your budget is meat versus everything else — holds up far better than the total does.
Does the list handle the shopping units?
That is the point of it. Every line shows what you need and then what to put in the
trolley — 3¼ lb becomes a 4 lb pack, 58 buns becomes eight packs of eight. Tick lines off
as you go; the ticks survive if you change a number mid-shop.