Now that we has the usual grade of feedback from the peanut gallery and Connor tried being more constructive, I'll do a bit of a breakdown. I actually looked at this angle before, but there are so many other, better ways to determine the power of the weapon I never bothered writing it all out.
1) Volume estimate. Not sure where you pulled that from, EvilleJedi of TFN and occasional poster here has done a lot of 3d rendering and estimates of a number of craft and found that an ISD is about 1e9 m^3.
2) Mass. Your math there is completely borked. You somehow multiplied it all by a factor of 10,000. Incidentally, that lowers the energy at the end, so it appears you basically underballed it. Using your figures it should mass 5.1155*10^10 kgs, or 51 million tons. Using a more accurate volume figure and an average density of water, a better mass figure would be 1e12 kgs, or 1 billion tons.
3) Energy figures. I calced out how much energy and power the jump to hyperspace took based of the run up, it is about 1e25 joules for an ISD. I posted the work both here and at SB with the expected results, including SBers demonstrating a refusal to grasp the idea of conservation of energy. As it is based off of film canon I would say it is a hardier standing, but if you don't wan to deal with that, there is quote you used. It is worth noting that as soon as a civilization hits the space age it is no longer a planetary civilization, as it now has (in theory anyways) access to all the resources in its system to sustain that civilization. So the average duration would basically be from the industrial revolution until the space age (IR as a starting point because prior to that energy consumption will be negligible by comparison). Thats in the low hundreds of years, so call it two orders of magnitude above the annual global consumption. For earth, that is about 1e20 joules. So for your civilization we are talking 1e22 joules. Given the mass of the ISD that's about 1e10 joules/kg to go to hyperspace.
For 1% of the earth to be put into hyperspace then requires ~1e32 joules. Enough to scatter its mass.
4) Source reliability. Again, we have the source of this quote being a gunnery master chief who by his own statements knows nothing about hypermatter, hyperspace, or how any of it works. This is pretty much useless.
5) Alternate estimates. Like I said, there are other, better ways to do it. Here's one of my faves; I've covered this before, but like Dr S details on his site, there is a shift in the placement of the planet/debris cloud in those frames.
Measurement of the apparent expansion of the Alderaan debris cloud provides further constraints on the properties of the Death Star's blast. The main debris cloud grows in a way that is slightly elongated in the direction of the incident beam. At late stages, the debris is clearly not concentric with the initial position of the planet. This suggests momentum transfer to a large part of the planetary bulk. Judging by the offset of the centre of mass before the beam strike and several seconds into the explosion, the mean recoil velocity of the ex-Alderaanian matter is on the order of 6.7 x 106 m / s in the plane of the picture, implying an impulse of 4.0 x 1031 kg m / s. A massless, light-speed beam delivering this amount of momentum would have a total energy of 1.2 x 1039 J. However this is an underestimate by some trigonometric factor, since the beam clearly was not parallel to the plane of the picture. Even so, the momentum-based estimate is in good agreement with estimates based on the apparent velocities of the expanding debris. The difference of one to two orders of mangitude is justified by the inefficiency of converting incident beam energy into kinetic energy of debris; much of the input energy is deposited as heat in the absorbing material.
so even if it does use some magic method to get around blowing it up, it still imparts enough energy to low it up, as shown by conservation of momentum.
Hope this helps.