Mine is about 17 miles of riding, or a little over 27 km.

This can vary by a few miles depending on where I'm coming from or where I have to be after to work. I have yet to take meandering detours in order to lengthen my rides -- I'm usually late for something so it's an unlikely scenario -- but I have been known to lengthen my routes by getting lost (once backtracked for at least a couple of km before realizing I'd gotten turned around).

C