When planning a party, you don't want to run out of food and beverages for your guests. To adequately plan, some calculations are in order. Use a recipe as the basis for your planning and then simple math will give you the amount needed. The rule of thumb is to plan for about 80 per cent of those invited to attend. If you are worried about not having enough, make sure to purchase a little extra.
Plan on each guest having two drinks in the first hour and a drink for every hour after that. For example, if you are going to have 25 guests and you plan on the party lasting four hours, estimate 50 drinks in the first hour and 25 drinks per hour for the last three hours of the party. (50+25+25+25=125 drinks)
Use your recipe to help you decide the quantities of liquid needed to buy. If your recipe makes 236ml servings for eight people, divide the 125 drinks needed by 8 to determine what multiple of each ingredient that you need to purchase. In this example, you need to make 15.625 (round up to 16) multiples of the recipe.
Multiply the quantity of each ingredient in the recipe by the same number (in this example, 16) to find how much to purchase.
Use cups in the same serving size as your recipe to prevent over serving your guests. Plan on making a drink for your party that you will drink afterward, if there are any leftovers. That way, if you purchase, the money and drink will not go to waste.
If serving alcohol, monitor your guests to ensure they are able to drive at the end of the night. Make sure one guest stays sober as a designated driver or call a cab to take guests home.