Drink quantities are arithmetic, not guesswork, and getting them right is worth real money in both directions: over-order and you have paid for a cellar, under-order and there is a queue at a bar nobody wanted. The inputs are your guest count, the hours, and what you are serving at each stage of the day, and the whole calculation can be done on one piece of paper.
The four moments you are buying for
A wedding has four distinct drinking moments and they consume very differently. The arrival reception is short and fast, and is where most of the sparkling goes. The meal is slower and is mostly wine, split by however your guests divide between red, white and neither. The toast is one glass each and is the easiest number in the whole calculation. The evening is the longest stretch and the least predictable, because it depends entirely on whether the bar is free or paid. Cost each moment separately with its own hours and its own guest count, because the guest count is not the same at all four: children and drivers are in some of them and not others.
What actually moves consumption
Whether the bar is free is the largest factor by a distance. A free bar roughly doubles evening consumption compared with a cash bar, which is worth knowing before you choose. Time of day is second: an afternoon wedding drinks less over the same hours than an evening one. Weather is third and it is real, since a hot day moves consumption towards beer, soft drinks and water in quantities people never plan for. Always order more water and more soft drinks than the calculation suggests. They are the cheapest thing on the list and they are what runs out.
Corkage, sale or return, and where the savings are
If the venue allows you to supply your own drink, ask the corkage rate per bottle before you compare anything, because a low headline hire fee and a high corkage can cost more than the alternative. Where you can supply, buy on sale or return if the merchant offers it, which removes the whole risk of over-ordering and is the single most useful trick in this part of the budget. Chill and delivery arrangements matter too: a pallet of warm wine arriving on the morning is not what you bought. Agree the delivery day, the storage and who is collecting the empties, since somebody has to and it should not be you on the Sunday.
Questions people ask about wedding alcohol calculator
How much drink do we need per guest?
Work it out per moment rather than per guest per day: arrival, meal, toast and evening each have their own hours and their own drinking guest count. That gets you far closer than any single rule of thumb.
Does a free bar change the quantity?
Substantially, roughly doubling evening consumption against a cash bar. Decide the bar model first, because every other number depends on it.
What about non-drinkers and children?
Count them out of the alcohol calculation and into the soft drinks, and then order more soft drinks and water than that suggests. Those are what run out on a warm day.
Is it cheaper to supply our own?
Often, once corkage is taken into account, and sometimes not at all. Get the corkage per bottle in writing and do the sum both ways before deciding.