From the department of party planning comes this common question: How much wine should you have on hand, per guest, for a sit-down dinner or holiday hors d'oeuvre party?
We picked up an answer and tips from The Baltimore Sun. They say that you should plan on about a half bottle of wine per guest for a sit-down dinner.
If you're only serving hors d'oeuvres, plan on one to two servings per guest, per hour. Check out the article for examples. (And always remember to have something special yet non-alcoholic for the designated drivers!)
Bacsac Bacsquare 04...

I followed the standard guidelines for alcohol per guest for our wedding. It didn't take into consideration a) that it was hot out and everyone wanted water b) it was in the middle of the day and c) all my husband's parents' friends were afraid to drink around them and seem like a bad Christian.
We were drinking the leftovers for a year. (And still have leftover Pepsi, yuck.)
Thanks for including the non-drinkers, dd's in your answer, you have no idea how often people look baffled when I say I don't drink, and then have nothing to offer but tap water. It costs like $2-3 for sparkling cider or something on that order. Not that its required but its so nice when people think about it.
I plan on 3 glasses per guest and always have just a touch leftover. It's better to over plan and have leftovers than run out. Also, it's great to keep some Cassis on hand in your liquor cabinet, a touch mixed with sparkling water creates and elegant non-alcoholic drink.
(At my wedding people drank 1.5 bottles per person; good thing we overestimated!)
ha!
For our wedding we went down our guest list and estimated who would drink how many servings of what (beer, wine, soda, water), and then rounded up to the nearest case.
For a dinner party, I think it's usually safe to have 1/2 a bottle per person, but I also like to have something non-alcoholic on hand.