I'm sure they are referring to the size of the frozen juice can, which I think is about 11 oz. At least that is what I use when I make it. And like gmc I may vary the amount of triple sec.
I usually do mine in a blender with ice instead of water to fill it. Makes great frozen Margaritas ready to pour. Put container in freezer after pouring first one and just bump it on the blender for the others. That is if you leave it in freezer long enough to get a little on the hard side.
But these are only good in South Texas where it is warm and you can set in lawn chair, maybe on the beach, under umbrella or shade, with good company.
Well,,, maybe good in other places also,, but still requires good company.
Jim M