A new study suggests that it should take just nineteen clicks to get from any randomly selected web page to any other web page. And if that reminds you of a Kevin Bacon meme, you won’t be surprised to know it’s human behavior as much as technology that makes this so.

The claim comes from Albert-Laszlo Barabasi of Northeastern University in a study published in Philosophical Transactions of the Royal Society. He specializes in network theory, both among humans and in tech.

19 clicks may seem a short maximum chain among an estimated 14 billion pages online, but Barbasi says two key factors make it work. The first is that its humans who decide what should go on a particular web page, and we tend to organize information in multiple logical ways. When we create a new page, we may categorize it as fitting into a particular topic, a geographical location, an organization, or any combination of these issues. This gives it a natural connection with several different types of other page, increasing the chance of a link between the two.

The other factor is the existence of aggregator sites such as Reddit which provide an indirect link between thousands of otherwise unconnected sites. They effectively act as directories rather than search engines, which aren’t counted: Barbasi was looking specifically at clickable links rather than having to type terms to continue the navigation.

According to Barbasi, it would only take the closure or disconnection of a few such sites to render the 19 click rule useless and make the web a lot less connected. With enough key sites down, the chains between some more obscure sites could be broken altogether.

Barbasi also found that the 19 click number scales rather than being proportional. In other words, you can take a “slice” of the web or you can extend the experiment to all of the trillion or so individual files that make up pages, and 19 still applies. He says there’s little reason to believe it won’t hold up as the web expands.

(The image above, courtesy of the Opte Project, shows the web back in 2005 with the most efficient set of direct links between sites. The colors indicate the type of domain for each site.)