Despite this many people seem to get it wrong! In particular “Chris Ridings of www.searchenginesystems.net” has written a paper entitled “PageRank Explained: Everything you’ve always wanted to know about PageRank”, pointed to by many people, that contains a fundamental mistake early on in the explanation! Unfortunately this means some of the recommendations in the paper are not quite accurate.

By showing code to correctly calculate real PageRank I hope to achieve several things in this response: Clearly explain how PageRank is calculated.

Go through every example in Chris’ paper, and add some more of my own, showing the correct PageRank for each diagram. By showing the code used to calculate each diagram I’ve opened myself up to peer review - mostly in an effort to make sure the examples are correct, but also because the code can help explain the PageRank calculations.

Describe some principles and observations on website design based on these correctly calculated examples.

Any good web designer should take the time to fully understand how PageRank really works - if you don’t then your site’s layout could be seriously hurting your Google listings!

[Note: I have nothing in particular against Chris. If I find any other papers on the subject I’ll try to comment evenly] How is PageRank Used?

PageRank is one of the methods Google uses to determine a page’s relevance or importance. It is only one part of the story when it comes to the Google listing, but the other aspects are discussed elsewhere (and are ever changing) and PageRank is interesting enough to deserve a paper of its own.

PageRank is also displayed on the toolbar of your browser if you’ve installed the Google toolbar (http://toolbar.google.com/). But the Toolbar PageRank only goes from 0 – 10 and seems to be something like a logarithmic scale: Toolbar PageRank (log base 10) Real PageRank 0 0 - 10 1 10 - 100 2 100 - 1,000 3 1,000 - 10,000 4 10,000 - 100,000 5 and so on… We can’t know the exact details of the scale because, as we’ll see later, the maximum PR of all pages on the web changes every month when Google does its re-indexing! If we presume the scale is logarithmic (although there is only anecdotal evidence for this at the time of writing) then Google could simply give the highest actual PR page a toolbar PR of 10 and scale the rest appropriately.

Also the toolbar sometimes guesses! The toolbar often shows me a Toolbar PR for pages I’ve only just uploaded and cannot possibly be in the index yet!

What seems to be happening is that the toolbar looks at the URL of the page the browser is displaying and strips off everything down the last “/” (i.e. it goes to the “parent” page in URL terms). If Google has a Toolbar PR for that parent then it subtracts 1 and shows that as the Toolbar PR for this page. If there’s no PR for the parent it goes to the parent’s parent’s page, but subtracting 2, and so on all the way up to the root of your site. If it can’t find a Toolbar PR to display in this way, that is if it doesn’t find a page with a real calculated PR, then the bar is greyed out.

Note that if the Toolbar is guessing in this way, the Actual PR of the page is 0 - though its PR will be calculated shortly after the Google spider first sees it.

PageRank says nothing about the content or size of a page, the language it’s written in, or the text used in the anchor of a link!

Definitions I’ve started to use some technical terms and shorthand in this paper. Now’s as good a time as any to define all the terms I’ll use: PR: Shorthand for PageRank: the actual, real, page rank for each page as calculated by Google. As we’ll see later this can range from 0.15 to billions.

Toolbar PR: The PageRank displayed in the Google toolbar in your browser. This ranges from 0 to 10.

Backlink: If page A links out to page B, then page B is said to have a “backlink” from page A.