How is one black hole is larger than another?

[htapps]

If black holes crush things into infinite density, shouldn't they all be the same size?

 

[Chronos]

Black hole size is expressed in terms of its event horizon, which is proportionate to its mass.

 

[Whovian]

(Note that when I say "inside a black hole," I mean "inside the event horizon.")

To elaborate, nobody really knows what on ... in the Universe happens inside a black hole, our current theories say they should collapse into 0 size, but some (a lot, from what I gather) think this just means our theories no longer apply perfectly in these situations.

So trying to describe stuff in terms of what's going on inside a Black Hole is going to be pretty much pointless, so we have to describe stuff in terms of what can be measured from outside the black hole.