Before buying any liquor, consider a number of questions that may help you determine quantities.

1. Where will the function be held? Cocktail parties and wedding showers are typically held at home. This means the cost of all refreshments would be the responsibility of the host or hostess. Rehearsal dinners and wedding receptions are usually held at a hotel or private club. If a cash bar were set up by the facility, your primary liquor expenditure would be for wines used during dinner, and for a toast to the bride and groom.
2. Will the gathering be formal or relaxed? A formal affair has a reduced pace which translates to a slower consumption rate. A relaxed atmosphere will have more life and encourage consumption.
3. How long will it last? The longer the event the more you'll have to buy.
4. How many guests do you expect? A larger group will consume more than a smaller group.
5. What's the average age of your guests? A younger group will consume more than an older group.

Unfortunately, there's no secret formula when it comes to making large liquor purchases. The best way to determine quantity is to divide bottle size by glass size. The approximate average will tell you how many glasses you'll expect to get from each bottle. The average wine serving is 4 ounces, with a mixed drink consisting of 11/2 ounces of spirits. For private functions plan on at least three to four drinks per person.

The chart below should help you determine your requirements.