I saw another name for viral growth factor K-factor<p>K-factor = i * c<p>i = number of invites sent by each customer (e.g. if each new customer invites five friends, i = 5)<p>c = percent conversion of each inbvite (e.g. if one in five invitees convert to new users, c = .2)<p><a href="http://en.wikipedia.org/wiki/K-factor_(marketing)" rel="nofollow">http://en.wikipedia.org/wiki/K-factor_(marketing)</a><p>Viral growth appears when K-factor > 1