It's an interesting expansion on the concept of the "k factor," a growth-hacking term borrowed from epidemiology. k = i x c, where i = invites per customer; c

It's an interesting expansion on the concept of the "k factor," a growth-hacking term borrowed from epidemiology. k = i x c, where i = invites per customer; c = conversion percentage on invites. It is sometimes referred to as the "viral(ity) coefficient." Essentially, k is the growth rate per customer. It is a sort of expected value of new users to be gleaned from each existing user. The equation in this blog post is slightly more sophisticated. It takes cycle times (the viral "incubation period") into account.