It would be about this big, the smallest black hole, and I base that on the fact that the gravitational mass of the sun is about 2 centimeters and this is a little more than that. But then at the other limit, what's the biggest black hole? I recall the first Texas symposium on relativistic astrophysics, Ivor Robinson, my imaginative Texas colleague at the University of Texas at Dallas, dreamed up this lovely title: Relativistic Astrophysics, to combine his love of relativity with something that was down to earth, practical, real observation - astrophysics. At this meeting the real eye-popper was a report by Maarten Schmidt of the discovery of what today we call Quasars. It was a newspaper reporter who was there at the meeting who dreamed up that short cut way of saying what Maarten Schmidt had been calling a Quasistellar Source. Today these bright spots at the center of some distant galaxies can only be understood as arising from the presence of a black hole which has enough broken down stars in orbit around it to give enormous luminosity. And how much mass are we talking about? We're talking about 5 million solar masses. So five million times this size. But if that's the biggest black hole, then we'll have to do quite a lot of looking before we know which of these quasars is the biggest. But in time we will have a reasonable guess.