system
Given the following post, respond as if you're commenting on Reddit:
human
If black holes are infinitely dense. How can they have different sizes?

I've heard that black holes have 0 volume and that they are infinitely dense. 

What exactly does this mean?

I know there is something I'm not getting because I've heard that black hole the size of a peanut would have as much mass as the earth. This wouldn't be true if all black holes had 0 volume.
gpt
The "size" of a black hole refers to an aspect of its gravitational reach, not it's physical size. The physical size of black hole is still infinitely small. The size of the event horizon (where space time is warped to the point that nothing can escape- aka it goes "black") is proportional to it's gravity, and thus its mass.