It varies a bit.

worst has been around 35 including the performers.
best has been just over 70 including performers.

It tends to fluctuate between those figures depending on holidays,festivals,weather etc.

70 is about my limit for the place.

I do tend to have a core audience consisting of folkies and non folkies (never been to a folk club until they came to mine)

Variety and entertainment and generally not having to listen to the same artist for too long seems to be the basis of why people come.