Question: How big is the black hole?

Abbie Hutty answered on 27 Feb 2020:

I don’t know which black hole you are asking about and I don’t know much about black holes anyway, but my understanding is that they are all basically single points, called singularities, so we can’t think of their size really as a distance from one side to the other; instead we have to think about how heavy they are.

So people talk about how much mass each black hole has rather than how big it is, often in terms of how many times the weight of our sun the black hole is.

But then there’s a thing called the event horizon- the distance from the black hole singularity at which light (and everything else) can no longer escape the black hole’s gravity, and will fall in- which is related to how heavy the black hole is. So this can kind of be thought of as the “size” of the black hole. But theories suggest that black holes can come in basically any size – there’s an interesting article here:

https://curiosity.com/topics/how-big-or-small-can-a-black-hole-get-curiosity/