The Drake Equation

N = f_s * f_p * n_e * f_ld * f_i * f_c * f_l
 

N = The number of communicative civilizations in the Milky Way

f_s = The number of stars in the Milky Way

f_p = The fraction of those stars with planets (Current evidence indicates that planetary systems may be common for stars like our Sun.)

n_e = The number of Earth-like worlds per planetary system

f_ld = The fraction of those Earth-like planets where life actually develops

f_i = The fraction of life sites where intelligence develops

f_c = The fraction of communicative planets (those on which electromagnetic communications technology develops)

f_l = The fraction of a planet's lifetime that has a technological civilization
 

If we substitute,
N = f_s * f_p * n_e * f_ld * f_i * f_c * f_l

_with

N = 400 billion (1/4) 2 (1/2) (1/10) (1/10) (1/100 million)

then

N ~ 10 technological civilizations in just the Milky Way Galaxy!
 

What would we do to determine the number of technological civilizations that exist in the Universe? Multiply this by 50-200 billion; the estimated number of galaxies in our Universe.

Click here for the Javascript version of the Drake Equation.