Even the fact that Kid Buu is a multi planet buster doesn't mean a thing, seeing that Hulk can climb out of a black hole at his highest levels, which has the power to level entire solar systems, to a range of galaxies if it is large enough. His energy attacks would likely be meaningless in the face of Hulk's durability at this point.
So I did the math:
Frieza's power level x4 = galaxy buster
Kid Buu = Frieza 1000+
1000 to 4 = 250+
So in short if Kid Buu used all of his energy he would have enough power to destroy 250+ galaxies. Quite impressive isn't it?