How many gallons of coffee do I need for 115 people?

A good rule of thumb is to plan on 1.25 cups (10 fluid ounces) per person. This allows for about two cups per person (some prefer more, some less) plus a little extra for refills.

115 people x (1.25 cups/person) = 143.75 cups of coffee

To convert cups to gallons, divide by 16.

143.75 cups / 16 cups/gallon = 9 gallons of coffee

To be safe, you may want to round up to 10 gallons. This will ensure that you have enough coffee for everyone, even if some people want extra refills.