# How many black holes exist?

How many black holes exist and what is their distrubtion over mass? There is a list of black holes, but I'm interested in an estimate of all black holes in the visible universe.

-
Supermassive black holes in particular? Why the supermassive tag? –  Blackbody Blacklight May 14 '14 at 13:57
@BlackbodyBlacklight no all of them including super-massive ones... –  draks ... May 14 '14 at 14:04

There exists probably about one supermassive black hole per galaxy, hence about 100 billion ($10^{11}$) in the observable universe.
If we take 1% of the stars ending as a black hole as a very rough order of magnitude estimate, we'll get about 1 billion stellar black holes per galaxy, hence about $10^{20}$ stellar black holes in the observable universe, give or take one order of magnitude.
Intermediate-mass black holes as presumed centers of globular clusters are harder to estimate, since there isn't much observational evidence. If the hypotheses turns out to be correct, and we take 1000 globular clusters per galaxy, we get about $10^{14}$ IMBHs.