User blog comment:Legionwrex/I figured out how many Reapers there are!/@comment-1978336-20120802110847/@comment-1900300-20120803154920

Only about 99% of the galaxy is actually habited due to the limitations of long distance space travel outside the mass relay network. You cant really get that far away from the relay and what amount of the network is used is limited due to the laws against activating new relays.