The size of the Bialetti coffee maker you choose depends on your brewing needs. The Bialetti Moka Express comes in various sizes, ranging from 1 to 12 cups. If you typically brew coffee for one or two people, a smaller size like the 3-cup or 6-cup model may be sufficient. For larger households or gatherings, a larger size like the 9-cup or 12-cup model would be more suitable.