A probabilistic assessment is made to determine the likely range of galactic civilizations. In order to define the
possible number of advanced galactic civilizations, the number of habitable planets is being determined with the help of a
newly formulated probability equation. This equation is expressing the number of habitable planets in terms of the assumed
galaxy size, the number of critical habitability criteria and the star and planet compliance rates with these criteria.
For effectiveness the equation uses instead of the individual compliance rates with the various habitability criteria the
geometric mean of the compliance rates with the criteria. This simplifies the calculational approach considerably and
makes it possible to obtain the necessary data to assess the extent of galactic habitability. These data are included in a Galactic
Habitability Table which presents in this way a complete overview of galactic habitability of a given galaxy as a
function of the number of critical criteria and the mean compliance rate with these criteria. While no scientific certainty
exists at present time for the exact values of these two parameters, zones of high probability can already be assessed. For
any number of habitability criteria assumed a minimum star and planet compliance ratio can be determined which is required
for the existence of advanced civilizations in a galaxy of any given size. As the next step the issue of concurrent
communicating civilizations has also been addressed.