Planning a wedding, birthday, anniversary and/or retirement party will require you calculate an approximate amount of alcohol to purchase. These numbers will vary depending on the type of party, the number of guests, time of the party and whether or not your guests have hotel and travel accommodations. It's always best to purchase a little more that you calculate to avoid running out at a time when the stores are closed. With the right amount of alcohol, your party will go smoothly.
Determine the number of hours the party will last.
Determine the average consumption rate per guest, per hour. The consumption rate will be a guesstimate based on the type of party, knowledge of your guests prior drinking habits and their accessibility to hotel rooms or transportation home. For a daytime party where the guests will be driving home, a good starting point is one drink per guest, per hour. For a wedding where the guests have hotel rooms within walking distance, a good average is two to three drinks per hour.
Multiply the number of guests (120) by the number of hours. Then multiply the result by the consumption rate per hour. This will give you the total number of drinks you will need to purchase.
Choose the type of drinks you would like to purchase based on knowledge of what your guests will like and what you would like to serve.
Divide the number of total drinks by the amount of drinks in one bottle of the type of alcohol you are serving. A typical wine bottle of 739ml can pour 5 drinks. For liquor, calculate one ounce per drink. For beer, a half keg has approximately 168 drinks. A good starting point is to purchase 1/3 of the total drinks in wine, 1/3 liquor and 1/3 beer.
Most guests will be happy with what ever you serve since it's free. For a function of this size, hire a professional bartender to assist with portion control and consumption monitoring.
You are responsible for the consumption of your guests. Provide access to taxi services to ensure your guests get home safely.