It’s considered to depend on the effective temperature of the black hole, which in turn is inversely proportional to, IIRC, the third power of the mass (there’s a proportionality constant, but I definitely don’t remember what it is, and I’m not going to go hunting for it at this hour).
What this means that a black hole with the mass of, say, the Sun, would be far too “black” for us to notice the feeble radiation coming from it (in fact, since its effective temperature would be far below the mean temperature of the universe, it would capture more photons from the background radiation than it emitted through the Hawking process, and thus increase in mass). A black hole with the mass of a small asteroid would radiate noticeably, however, and “evaporate” via the Hawking process over the lifespan of the universe to date (thus putting paid to Hawking’s earlier notion that there would be “quantum black holes” left over from the Big Bang. They might have been created, but they’ve also since gone away). A very small black hole would, from our perspective, vanish almost immediately in a burst of (very) hard radiation (at one time, it was thought that this explained so-called “X-ray bursters”, but this is now considered to be wrong).