just to put them all too the same scale
in Gallons:
Nimitz Class - 3,500,000
Wasp - 460,000
Cavour - ~395,000
JC1/Canberra - 240,000
those all sound about right to me, the America class should be interesting, without the well deck there will be much more fuel space
I have seen some reference's to the America Class having around the 1 mil mark