Size of black holes and how they're measured

[gbrak30]

So if black holes are infinitely small, how can they have a diameter?  I prefer asking people rather than google, since this can be more of a philosophical question
Well, I have never seen a diameter but mass i have seen, but still, how do you measure the size/mass of something you cannot observe directly and that is theoretically infinitely small?

[codefantastic]

the black hole itself isn't infantly small, the singularity at the center is.

[Darvince]

the diameter of a black hole is defined as the diameter of its event horizon as the singularity itself has no size as far as we know

[vh]

to add, mass is measured by velocites of orbiting bodies, and the event horizon can be computed from mass

[fredetuc]

Well lets say this u can make a black hole out of anything as long as you shrink it down to microscopic size but keep the same mass. Don't quote me on this but i'm 89% sure.