According to my research, a moka pot "cup" refers to a fill volume of around 60 milliliters (2 fluid ounces) -- at least for a Bialetti. Theoretically, a "cup" is, therefore, a double espresso. Still, the exact milliliters don't matter. It's much more important to buy an espresso maker that matches your actual consumption per brew. Generally, the smaller the maker, the better the results, and that's only if you fill it to the brim every time -- especially with regard to the ground espresso. So, a two-person household certainly doesn't need an 18-cup stovetop espresso maker.