I don't think most people would say there's a maximum number, beyond which they'd regard their repertoire as complete. It's the minimum number that's of more interest: how many songs do I need to know in order to keep people's interest when I sing?

And this depends largely and how often and where you perform. If I go to see a professional, paid artist at a club, I don't expect him to do exactly the same set he did when he came there a year or two ago. A good pro will keep developing his repertoire, and probably have something quite new every time that he's excited about and keen to share. This needs dozens or even hundreds of songs as a working repertoire.

If you just sing a song or two in a floor spot or a session or a singaround, you don't need so many songs, but it's nice to be able to rise to the occasion and find something suitable for the occasion (e.g. season, recent events, weather, etc). Sometimes at a song session, a "theme" develops spontaneously, and people try to find something that fits. There is, however, always someone who will say, "I don't know any songs about the sea/the spring/Brexit, so here's a Tom Paxton song"; this is probably the song he sang last week or the week before, from his four-song repertoire. Yawn. This is when I go to the bar or the loo.

So even for the occasional singer, a good, varied repertoire of a couple of dozen songs is what I'd consider a minimum. People often start by singing the only song they know; fair enough, and then they go home and lear another one for next time, and so it builds up. But for most of us, there's no point at which you ever want to stop. I know dozens of songs, but have just found a gorgeous tune to "The Lark in the Morning", collected only a few miles from where I live in Devon, so that's next on my list...

Marje