Google isn't providing any good solid answers on this; what is the rate of thermal shrinkage you are all experiencing when measuring your hot wort final volume vs. your cooled worts final volume?
For pure water at 100 degrees C (boiling) and standard atmospheric pressure the specific volume is .001044 m^3/kg, and .001003 at 25 C (about 77 f) which would be 3.93% ((.001044-.001003)/.001044) without taking into consideration all the dissolved sugars (which I don't think contribute too much to it.)
Got my info from Chemical, Biochemical, and Engineering Thermodynamics 4E, Stanley I. Sander
haha I knew I'd get some kind of use out of my chemical engineering books