How to use it
Put in how many guests are drinking alcohol and how many are not. The answer updates as you type. Then go through the other boxes and change anything that doesn't fit your day: a longer evening, a second glass for the toast, a larger wine glass.
Our starting figures
The numbers already in the boxes are our guesses, not rules or averages from a survey. We start at one glass of fizz on arrival and one for the toast, two glasses of wine with the meal, one drink an hour through a four-hour evening, a 125 ml fizz glass, a 175 ml wine glass, a 750 ml bottle and 10% spare. Your guests know their own habits better than we do, so change them.
How it is worked out
Glasses each, times guests, plus the spare, gives the glasses. Glasses times the pour in millilitres, divided by the bottle size, gives the bottles, always rounded up. The evening comes out as a count of drinks, because a bar serves all sorts. Soft drinks use the same glasses each as everyone else, so nobody is left with an empty glass for the toast.
Next: the cake portion calculator and the planning checklist.