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Glossary Definition: PageRank

An ever-growing glossary of SEO Jargon

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What is PageRank?

PageRank, or PR is an algorithm that Google uses to analyze link distribution and connectivity of every website on the Web.

The PageRank algorithm assigns a numeric value from 0 to 10 to every page in its index, which represents how "important" it considers that page. PageRank is calculated by looking at a web page's backlinks, with each link contributing some amount of its own PR.

PageRank is one factor that determines a web page's ranking in Google's search results; however, it has significantly less of an impact than it did several years ago, and is just one of over 200 signals that affect how a website is crawled, indexed and ranked

Named after Google co-founder Larry Page, the original PageRank algorithm was one of Google's early innovations, instrumental to its early success.

PageRank Concept

PageRank is a probabilistic concept used to represent the likelihood that a person randomly clicking on links will arrive at any particular page. Google considers each link to a web page as a vote; therefore, the more votes cast for a page, the more important the page must be. Pages with many votes and high PageRank will pass along more PR through links.

PageRank is calculated on progression similar to a logarithmic scale. Considering, for the sake of simplicity, that all links are of equal value, this can be demonstrated in table 1:

PageRank (log base 10) Votes
0 0 - 10
1 10 - 100
2 100 - 1 000
3 1000 - 10 000
4 10 000 - 100 000
5 etc
Table 1. PageRank Logarithmic scale

PageRank Algorithm Keypoints

Google PageRank is a sophisticated algorithm that has evolved since its original version. While most of the mathematical details behind PageRank are unimportant to search engine optimization, some points are worth noting:

  • PageRank is calculated on a logarithmic scale: Therefore, the difference between PR5 and PR6 is much greater then the difference between PR3 and PR4
  • Web pages only pass a percentage of their PageRank: A page's maximum passable PageRank through an outbound link was once 85% to 90% of its own PR, and less for internal links; however, this percentage is likely lower today
  • Votes do not have equal weight: Passable PageRank is divided among the number of links a page points to. A backlink from a PR4 site with 3 outbound links would be more valuable than links coming from a PR6 site with 500 outbound links.
  • New PageRank values are only made public every few months, with changes reflected on Google's Toolbar PageRank, although PR is continuously being updated
  • PageRank is just one of many ranking signals: PageRank is an easy metric to monitor; however it says little about a website's trust and authority; which say more about ranking potential

Summary

Many feel that PageRank is now almost irrelevant—and justifiably so— as Google's ranking algorithms have grown far more sophisticated over the years. As a signal, PR can still be useful for quickly spotting sections of a website where link juice isn't flowing as it should.

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