Why the bar runs dry at 9pm

Running out of drinks is the failure guests remember longest, and it is almost always an arithmetic problem rather than a budget one. Consumption is not steady across a night, and most orders are built as though it is.

The curve is front-loaded

Guests drink hardest in the first ninety minutes. Arrival and canapés account for a disproportionate share of the night's total — people are standing, socialising, nervous, and holding a glass is something to do.

Consumption drops through the meal, rises again when dancing starts, then tails off. If you order on a flat average you will be short exactly when the bar is busiest, which is also when a queue is most visible.

A workable planning figure: two to three drinks per person in the first hour, then roughly one per person per hour after.

Sparkling goes faster than anyone plans

On arrival, most guests take sparkling, whatever their usual preference. The same happens for a toast. Both moments consume far more than a proportional share, and both are when running out is most conspicuous.

Order sparkling as though it is the main drink for the first hour, because it is.

Packages and consumption are different risks

A package caps your cost and caps nothing else — the venue manages supply. On consumption you pay for what is drunk, which is cheaper with a light crowd and considerably more expensive with a heavy one.

The question that decides it: do you know your guests? A hundred people you know well are predictable. A mixed corporate crowd is not, and a package removes the variance.

If you go on consumption, set a spend ceiling and name the person who will be told when it is approached. Not the couple.

Service points, not stock, cause queues

One bar for 150 guests produces a twenty minute queue at 9pm no matter how much stock sits behind it. Two service points, or roaming trays through the first hour, matter more than the order size.

Roughly one bartender per fifty guests is a serviceable minimum, and more at peak.

The things that quietly run out

Ice, soda water, tonic, lemons, and non-alcoholic options. Every one of them is cheap and every one of them is routinely short. Non-alcoholic in particular is under-ordered by venues working from old assumptions — order properly, and guests who are not drinking will notice that somebody thought about them.