Photo by GorillaSushi,, CC BY-SA 2.0

Every now and then, we hear or read the advice that taxonomies should be no more than three levels deep. The reason given is what’s commonly known in the web design world as the three-click rule. Supposedly, users do not have the patience to find information on a website using any more than three clicks of a mouse. Ergo, navigation hierarchies and similar structures are expected to honor this limitation by keeping the entire pool at kiddie depth.

A quick web search shows that the rule has received wide credence and distribution. Is it valid, though? And does it apply to taxonomies?

There have been doubters. In 2009, usability consultant David Hamill wrote a strong (albeit gruesome) statement about the rule:

The 3-click rule is the Freddy Krueger of web design advice. You think it’s finally dead and then it comes back and starts slashing up sensible debate about usable design. I’m hoping to convince you to stop talking about the 3-click rule. I don’t mean substituting it with the 4-click rule or the 5-click rule. You should stop counting clicks as a measure of usability altogether. [Hamill’s emphasis]

Hamill continues:

In 2003, Joshua Porter of User Interface Engineering wrote an article that should have killed the 3-click rule for good. He found that the number of clicks affects neither task completion nor user satisfaction. …

Once the 3-click rule had been disproved, you might expect click counting to fall out of fashion. But alas it hasn’t.

Joshua Porter’s article, Testing the Three-Click Rule, was originally published in April 2003. In it, Porter explains the research that his team conducted, and the findings that they uncovered. One of the more basic findings was that “Hardly anybody gave up after three clicks.” People were willing to click as many as 25 times to find what they were looking for. He concluded,

We can’t be overly critical of a rule that has the effect of helping designers keep their focus on users and their needs. However, the Three-Click Rule does not focus on the real problem. The number of clicks isn’t what’s important to users, but whether or not they’re successful at finding what they’re seeking.

Interface designer Ally Reeves elaborates on the findings, with an interpretation that argues for logical, intuitive, and moderately deep hierarchical structure:

What if your navigation structure gracefully leads users beyond 3 clicks into a 5 click navigation that gets them to the right place? Or more than 5 clicks?

Never fear. Research shows that if the progressive revelation of information takes the user down a path towards refinement that feels like progress and gets them where they need to be, they will give you up to twelve clicks before turning grumpy. Yes, twelve.

And that’s about the maximum depth for a typical science or humanities taxonomy or thesaurus. And that’s about the depth that’s needed in order to offer the degree of granularity or specificity that researchers require.

So if there’s no solid basis for the three-clicks rule, where did it come from in the first place? The answer surfaced in a blog post last June by Martin White, who revealed that Dr. Peter Cochrane, an Internet technology pioneer, was the originator. White explains:

The three clicks rule was proposed by Peter around 1998/1999 and had nothing whatsoever to do with navigation structure optimization. Peter was a telecoms engineer and his concern was over bandwidth latency as the use of the Internet increased but was still largely running over copper and not optical fibre. It was typically taking 15-20 seconds for a page to load in response to a click and so three clicks might take a minute to complete. …

His concern was that unless there was a significant network capacity upgrade world wide the delay for a user even needing as few as three clicks would be such that they would give up the task, and that as a result the Web might never fulfil its potential. He wrote this around 1998:

“Who would like a three click, one second, no handbook world? Drill down to anything you want in three clicks of a mouse, and it appears on your screen in under a second! No need to read a handbook, no training – just the application of intuition – an obvious and easy to use interface for everyone. The only prospect of realising this dream relies on ‘end-to-end’ optical fibre and significant improvements in network and computer protocols, interfaces and software.”

This is just to put the origin of the three clicks rule on the current record and hopefully to stop people wasting their time trying to prove or disprove a half-remembered proposition.

So don’t think that you have to limit your taxonomy or thesaurus to three or perhaps four levels. People are willing to dig deeper, as long as they have reason to think they’re getting somewhere.


Photo by Charles Knowles, / CC BY 2.0

Barbara Gilles, Taxonomist
Access Innovations, Inc.