I've been trying to remember this recently (being too lazy to check my logbook!). I would say, ballpark figures, maybe 10hrs in the circuit before first solo, on average (excluding go-arounds, orbits, etc...) about 6 circuits per hour. So that's 60 circuits.
I'm prepared to be corrected, but this seems reasonable to me.
But as has been said, it's all about quality, not quantity. I'm going through it all again at the moment doing a tailwheel conversion and I've prepared myself for an indefinate number of circuits! On any given circuit I'm getting at least one thing wrong, nearly always including the landing. As a result I'm getting comments from my instructor on a regular basis (though only one major correction so far!) and so I accept that soloing is a way off yet.