It's not about lines of code it's about the number and type of problems solved. I have spent days looking for a solution when all I needed to do was change a single constant. I have also written hundred of lines of code whole hog, been surprized that it compiled without errors, and shocked that it was bug free. Yet, I have no idea what was more usefull.

Spending a few months working on hard problems without a functional debugger can compleatly change how you aproach programming. But, so does finaly understanding how to use a debugger. Spending a few weeks reading other peoples code to document a working system was also an incredably valuable experence.

PS: The closest thing to a single nuber I can think of is "how many diffrent months of experence do you have?"

I think it's just too difficult a problem to distill down into a single metric. I did CS and Math for my undergrad and I was in the PhD program for CS but left with my MSc. My focus was on design and analysis of algorithms and based on that training, in my 3 years of professional activity (2 at a NASA contractor) I've run into very few problems that compared to the kind of work I did in my thesis. I think lines of code is one metric - but a really high number could actually be a sign of a really bad programmer! So, it's an inherently noisy signal. I think you have to look at successful projects completed and individual roles in those projects and judge that way.