Yep it is 12 Q exactly. It is easiest to just buy three gal. jugs of cj-4. The 5 gal. bucket is cheaper, but a bit harder to measure out. Of course I am speaking of Rotella T because that is all I use.
Finally, some jack-donkey designed something to come out evenly! 3 one gallon jugs. Nothing simpler! Not like my wife's sequoia....6.5 quarts...dayum japs.