Have you gone viral?


So many times I hear marketeers expressing their dream of commissioning creative content that would be considered viral marketing, but at what point has something successfully gone viral? Well, here is one measuring tool… it’s called the k-factor.

This model comes from epidemiology and measures infection rates: essentially how many new users does each new user beget. The standard formula for k-factor is: A k-factor, greater than 1, indicates that a product has ‘gone viral’. So the goal is to target a rate greater than 1. In practice, many successful social networks have had growth below 1 e.g. DropBox. As such, one would target a k-factor between 0.2 & 0.7.

But you also need to consider the cycle lengths for each viral sequence i.e. on average how long does it take for a new user to send out invites, for those invites to be opened and accepted. Putting this and K-factor together you can project growth/spread of the content. Easy peasy lemon squeezy.


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Marcus is a Creative Director with over 15 years London experience. Client experiences includes BBC, Timberland and Coca Cola. Marcus is a member of the Typographic Circle and D&Ad. A passion for playing cricket, exploring the Devon coastline and collecting 1950s cigarette adverts.


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