Cocktail parties
Plan on half a bottle of wine per person per two-hour period.
If guests will be serving themselves, plan for 10% more wine.

Dinner parties
Each 750ml bottle of wine provides about 5 servings of 5 ounces each or 6 servings of 4 ounces each.
If you are planning wine with a meal, plan 1 to 1.5 servings per course per person.

How to calculate the number of bottles you require of each wine
Multiply the number of people you plan to serve by the number of glasses on average that each person will drink divided by 5 (or 6 if you prefer a 4 ounce pour).

What type of wine to serve
If you expect the weather to be warm and your event is outside, or if your event is before 5:00 p.m., plan on 70% white wine, 30% red wine. Otherwise, plan to serve 40% white wine and 60% red wine.