Drake equation defines a "civilization" as a species possessing interstellar communication capability. This means radiotelescopes. By this definition, civilization did not appear on Earth until the 1930s. Although, Earth does not really have the means to usefully broadcast and had limited means to interpret interstellar radio communications. Also, we may need to look at laser or other forms of interstellar communication.

L is the average lifetime of a technological civilization.
N/L, is the rate at which such civilizations are disappearing from the galaxy.
R∗, the rate of star formation in our galaxy;
fp, the fraction of these stars that have planetary systems;
ne, is the mean number of planets in each system that have environments favorable to life;
fl the fraction of these that actually developed life;
fi the fraction of these that evolved intelligent species; and
fc the fraction of intelligent species that developed sufficient technology for interstellar communication

If we estimate L=50,000 years (ten times recorded history), R∗ = 10 stars per year, fp = 0.5, and each of the other four factors ne, fl, fi, and fc equal to 0.2, we calculate the total number of technological civilizations in our galaxy, N, equals 400.