How Can We Determine the Size of a Black Hole?

[fillipeano]

Is there any way to determine how big a black hole is? I googled the question but I didn't find any answer.

 

[Ich]

If you mean its diameter, you can determine it theoretically from its mass:
1 solar mass = 5.9 km,
1000 solar masses = 5900 km and so on.
AFAIK, there are no actual measurements of a diameter. Maybe within the next 10 years, they will have measurements of the BH in the center of the Milky Way.

 

[Chronos]

Black hole size is usually expressed as the size of its event horizon, which is pretty easy to calculate.

 

[jnorman]

yes, but it should be noted that the EH is an effect caused by the BH. the actual BH itself has no size, ie, the singularity proper has zero volume.

 

[qraal]

yes, but it should be noted that the EH is an effect caused by the BH. the actual BH itself has no size, ie, the singularity proper has zero volume.

That's only if a certain picture of black hole interiors is correct. Several different theories are available with quite different outcomes. Thus the event horizon is the boundary as far as we know or close to.