It takes about three to four gallons of chili to feed 40 people as a main dish. Most chili recipes consider a serving as 1 cup to 1 1/2 cups, and there are 16 cups in a gallon.
To determine a more precise amount when serving chili to a crowd, consider the number and eating style of the guests. Opt for a greater amount if big eaters are being served; choose less if children or people with smaller appetites are eating. Less chili is needed if it is a particularly hearty recipe or if several side dishes are on the menu.