Buying wine: How much do you need?
Here's a perennial social question: How much wine should you buy?
It's always hard to predict how a crowd will behave, and a lot depends on whether your friends like to drink, how many of them prefer wine, beer or liquor, how long the party will last, and so on.
But by working with a few basic principles, you can usually come up with a good estimate. The standard "fifth" wine bottle, now turned metric at 750 ml, contains enough wine for five 5-ounce glasses, a fairly standard serving. If you assume that half of your guests will want wine, and that they'll average two glasses each (some drinking only one, others three or four), then you have a starting point for calculating your shopping list.
So, if you're inviting 90 pals to a holiday gathering, you might assume that half of them will take wine; figure an average of two glasses for each and you get 90 glasses, which divided by five makes 18 bottles or 1 1/2 cases of 12. I'd err on the high side by purchasing two cases (choosing a store that offers a discount for case purchases). Beer for the rest -- assume three bottles each -- and soft drinks for the teetotalers in attendance. The chances are that you'll have leftovers to stock your bar; but if you're thrifty (and if local laws permit), you might ask in advance if the wine shop is willing to take back unopened bottles.