How much root beer and ice cream for 40 people?

To serve root beer floats for 40 people, a good estimate is about 1 cup (8 ounces) of root beer and 1 scoop of ice cream per person. This means you'll need approximately 2.5 gallons of root beer (40 cups) and 40 scoops of ice cream, which is roughly 2.5 to 3 quarts, depending on scoop size. Adjust quantities based on individual preferences and serving sizes.