How many “loyal” fans do musicians need to have to make a living from music?

Of course, it's impossible to say exactly, as it also depends on what the consumer should/has to pay to listen to their music. Not to mention radio or advertising revenue on the internet or elsewhere. But, roughly speaking, I'd be interested to know how many fans are willing to buy albums, individual tracks—stream them, for example—attend concerts, buy merchandise, or buy special albums with "reissues" so that the band/artist earns enough to be able to live off the music.