N = Star_Rate x f_planets x f_habitable x f_life x f_intelligence x f_communicate x Lifetime

Equation Explained

N = Number of Civilizations that can communicate with us

Star_Rate = Star Formation rate in our Galaxy

f_planets = Fraction of stars that have planets

f_habitable = Fraction of Planets per star that can support life.

f_life = Fraction of Planets that develop Life

f_intelligence = Fraction of planets with life that develop intelligent life

f_communicate = Fraction of intelligent life that is willing and able to communicate

Lifetime = Expected lifetime of civilizations