Step1. Determine how many wine drinkers will be in attendance for the event.

Step2. Multiply the number of wine drinking guests by the length of the event in hours. This number represents the approximate number of drinks needed for the event. For a three-hour gathering with 25 wine drinkers in attendance, this number would be 75.

Step3. Take the number that represents the wine servings needed for the event and divide it by five, which is the average number of servings from a 750 ml wine bottle. Using the example from the last step; 75 drinks divided by 5 servings per bottle would equal 15 bottles needed.

Step4. Always round up when estimating the number of bottles needed. Bringing an additional 20 percent more wine above your estimate will help ensure that there will be enough for even the heavy drinkers. For our example, this would mean an additional two bottles of wine. (Multiply your original estimate by 0.2 to calculate how many extra bottles you will need, which comes to one bottle extra for every five bottles in the original estimate.)