So.. recent estimations for the Drake Equation (Maccone, 2012) suggest that there could be around 4,600 civilizations in our galaxy that are able to release detectable signals.
I find this number a little bit excessive, so I plugged some of the values of our Solar System into the equation and I obtained a smaller yet more realistic result, in my opinion: 50 civilizations.
Just in case someone is interested, I made a video showing the values I used:
http://www.youtube.com/watch?v=j2AIWIcn7Ig&t=5s
Do you think 50 is a more realistic number?