400,000,000,000
it had been estimated that the approximate number of stars in the galaxy was about 400 billion. Around half of these had planets which support some form of life. Some ten percent of these planets developed life on their own, and one in a thousand of these worlds developed sentient life. These rough calculations revealed that there were about 20 million forms of sentient life to be found in the galaxy. Note that The Last Command indicates that there were just a hundred billion stars in the galaxy.