Average Weight of Human Head

I couldn't find any references for this online, so I asked around my workplace (the Department of Anatomy & Histology, University of Sydney). The most convincing response came from the service room where the technical officers actually cut up the bodies:

"An adult human cadaver head cut off around vertebra C3, with no hair, weighs somewhere between 4.5 and 5 kg, constituting around 8% of the whole body mass."