No, I divided all right
My mistake was much more boring: I misplaced my decimal commas when consulted the density table, so result got about x1000 times more impressive
But now we have the directly opposite problem: while Stone Colossus not so dense (and, certainly, should be able to float) - from what, exactly, it's made of?
Even lightest pumice is almost x10 heavier! (More like ~8.39 times, but still...)
(And yes - I know creatures not always occupy all of their "Space". I used it when presumed Stone Colossus was actually dense - since it have DR - because it would be not just easier to calculate, but also make the final result lower. Now, when we see it's, actually, ultra-light for its size and material - how much smaller of a space should it be for more "real" results?)