Yeah, I use everything from 7 gallons on down to 3 liters, you can
never have too many. I finally started marking how many bottles each
carboy holds, I have some 5 gallon carboys that hold over 26 750 ml
bottles, most hold 25.5. I really like the little 3 gallon carboys
too; they take up very little space and can be used to split batches
so you can experiment.

Joe