How much do I need to buy for the bar?

The catering standard is one drink per guest per hour for the first two hours, then half a drink per guest per hour after that. For 60 guests over 5 hours: (60 × 1 × 2) + (60 × 0.5 × 3) = 210 drinks, or 3.5 drinks per guest across the event. Adjust for format: a cocktail party with no seated meal runs about 15% higher, a food-led casual party about 15% lower. That rate is an average across the room — some guests will have none and some will have six.

A 750 mL bottle pours five standard 5 fl oz glasses. If wine takes half your drink total, 210 drinks means 105 glasses, which is 21 bottles. Round up, always. For a wedding, add one extra glass of sparkling per adult for the toast — a bottle of sparkling gives about six smaller toast pours. Most retailers will take back sealed, unopened bottles, so buying a case beyond the estimate is usually a free option worth asking about.

At a 4-hour casual party, 50 guests come to about (50 × 1 × 2) + (50 × 0.5 × 2) = 150 drinks, adjusted down 15% for the food-led format gives about 128. If beer takes half of that, you need 64 cans, which is three cases of 24 or eleven six-packs. Buy in cases — the per-can price is almost always lower and unopened cases store fine.

A standard drink of spirits is 1.5 fl oz, which is about 44 mL, so a 750 mL bottle yields roughly 17 drinks and a 1.75 L handle about 39. For 100 guests over 4 hours the total is around 300 drinks; if spirits take 20% of that, you need 60 drinks, or 4 bottles. Then buy mixers at roughly three parts mixer to one part spirit — a liter of mixer covers about six drinks, so 60 spirit drinks want about 10 liters of soda, tonic and juice.

In the United States a standard drink contains 14 grams of pure alcohol. That is 12 fl oz of regular beer at about 5% ABV, 5 fl oz of wine at about 12%, or 1.5 fl oz of 80-proof spirits at 40%. All three are the same amount of alcohol, which is the whole point of the definition. It also means a 16 oz craft IPA at 7% is closer to two standard drinks than one, and a generously poured cocktail can easily be three.

Because arrival drinking is a real and consistent pattern: guests arrive, get handed a drink, and finish it quickly while the room fills and there is nothing else to do. After the first two hours people are eating, talking and dancing, and consumption settles to roughly half the arrival rate. Planning at a flat rate for the whole event either leaves you short in the first hour or leaves you with a lot of leftovers.

Count everyone, not just non-drinkers: plan roughly one non-alcoholic serving per person per hour on top of the alcohol, and more in hot weather. A 12-pack covers twelve 12 fl oz servings. Water in particular is always underestimated — alcohol is a diuretic, and a daytime outdoor event can go through more water than beer. Set out water where people can help themselves rather than making them ask.

About 1 lb (0.45 kg) per guest for drinks alone, and double that if you are also chilling bottles and cans in tubs. Buy it the morning of the event: bags stored in a home freezer fuse into a single unusable block within a day or so. If you are chilling drinks fast, a bucket of ice, water and a handful of salt cools cans in about 20–30 minutes, far faster than ice alone.

They will not, and the model already accounts for it — these are averages across a room, validated across a lot of events. Where it breaks down is at small parties: with twelve guests, three heavy drinkers can double the real consumption and the average stops being useful. Under about twenty guests, plan for the people you actually know rather than the rate. Above that, the averages hold up well.

In most US states, potentially yes. Social-host liability laws generally hold a host responsible for serving alcohol to anyone under 21, and many states extend that to serving a visibly intoxicated guest who then causes harm. The specifics vary a lot by state. Practically: check IDs if you are unsure, stop serving anyone who is obviously impaired, close the bar an hour before the end, and have coffee, food and a way home available.

About 2 liters of popped popcorn per person per two hours of runtime, and half a liter of drink over the same window. For four people watching a 150-minute film that is 10 liters of popped corn — which sounds enormous until you remember popcorn is mostly air, and 10 L of popped volume comes from only about 100 g of kernels. Add a bag of chips per two people, and a second snack round at the midpoint for anything over two and a half hours.

For wine and beer, yes — sealed bottles and unopened cases keep indefinitely, and many retailers accept returns on unopened stock, so the downside of over-buying is close to zero while running dry ends the party. For anything perishable or opened, buy to the estimate. And build the buffer into the categories people actually drink first: at most events that is beer early and wine late.