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Glossary Definition: PageRank

An ever-growing glossary of SEO Jargon

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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