7.3 pounds per gallon, 55 pounds per cubic foot.
68 trillion X 7.3 = say 500 trillion pounds (rounded off)
500 tp / 55 (per cu-ft)= 9 trillion cubic feet
1 cubic mile is 147,197,952,000 cubic feet
9,000,000,000,000 / 147,197,952,000
roughly 1323 cubic miles or a cube of 11X11x11 miles.
any corrections for gross discrepancey?
doesn't seem like a huge number considering?
regards
mech