throw out the volume number, don't even look at it!
I have no idea how the manufacturers measure it (cad, filling with water, Ouija board, guess, what sounds good???) but I'd be willing to bet real money not one in ten is correct, damn half the weight measurements are off and you'd think that should be easy enough...volume, forget about it.
In my experience the only sure way to know if a boat will fit you is to sit in it and the way to know if it will work for you is to paddle it a few times.
That being said, by all means look at the specs but only as a guide for what boats to demo not as fact.