generally speaking, when recipes call for a "cup" of greens, it is an estimate of the amount of chopped greens that would fill a cup without packing it in.
After you make green smoothies a while you won't need to actually measure the greens as you will have a good idea of the amount you want to put in. The amount of greens you put in is all about taste. As you get accustomed to the flavor of the greens you use you can add more.
