Measuring total amount of Bitcoin in circulation Since fractional reserve banking where money is created by lending is possible with Bitcoin is there a way it can be measured to give a total amount of money in the system? Such a measurement would actually reveal the value of money multiplier which I define as a real statistical ratio between commercial banks money and monetary base rather than a theoretical maximum ratio that is legally defined (because of lack of regulation with Bitcoin).

I guess such a measurement can either be direct (by lenders reporting how much they've lent) or indirect (measuring some other impacts those loans have on economy).
The concept of a money multiplier is meaningless in an unregulated environment. The money multiplier is, by definition, a legal limit imposed on the reserves banks must have.