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Google PageRank and How To Get It
by Bob Wakfer ©Copyright 2004

PageRank: The Background

Google's PageRank (PR) is one of the most sought after, and yet 
misunderstood web page attributes. PageRank, named after one of 
the founders of the Google search engine, Larry Page, was the 
innovative foundation that the Google search engine was built on.

The theory was that a link from one web page to a web page of 
another site was in essence a vote for that page. The reasoning 
was that webmasters would only link to pages that they thought 
were interesting and of value to their viewers. Google used the 
number of inbound links (IBL) to a page to judge the importance 
and relevance of that page, and based on this calculation, and 
other factors, decided where to place that page on the search 
results page (SERP).

They devised a scale of measurement for PageRank from 1 to 10. 
Then for the information of webmasters and interested people 
they produced a toolbar that can be deployed in Internet Explorer 
that indicates the PageRank value of any page being viewed in 
the browser. These values have become known as PR0 to PR10.

Since PR values are a result of IBLs, Google decided to give 
them their own name and refers to inbound links as backlinks. 
As part of the toolbar there is a quick lookup of the number of 
backlinks that Google reports for the page that is currently 
being viewed in the browser. This search can also be done 
without the aid of the toolbar by simply typing 
"link:http://www.yourURL.com" into the Google search box.

The one trick to this link search is that Google does not 
display all backlinks. At one time it was thought that they only 
listed pages with a value of PR4 or greater. Today however, you 
will find backlinks reported from pages of lower PR values. So, 
at best, Google's backlink search seems to present some sample 
of pages linking to the site. Suffice it to say that this search 
is not a reliable measure of all IBLs to a page.

How is PageRank Calculated?

In simplest terms PR is calculated by the sharing of PR from 
all the IBL links to your page. This is not strictly accurate 
because Google also uses the internal links within a site in 
the calculation of PR. Each link to a page carries with it and 
passes PR value to the target page. The PR points or value 
passed depend on the PR value of the page they come from, and 
the total outbound links from the page. It is generally agreed 
that a page will only pass about 85% of its value to the page it 
links to. So a PR5 page with a single outbound link will pass 
85% of the value of a PR5 page to the page it links to.

But virtually no page has only a single link -- remember 
internal links are also used in the total outbound link 
count -- so the value passed to any page is 85% of the PR, 
divided by the total number of outbound links.

The question now becomes what is the PR point value of the 
different PR levels. Most observers believe that the relationship 
between PR levels is logarithmic rather than linear. In other 
words PR5 is not worth 25% more than a PR4, but may be worth 
4 to 6 times more.

It is also understood that a PR value is not a single number, 
but is in fact a range of values. So not all PR6s are equal. As 
the chart below shows a PR6 may be just on the upper boundary of 
a PR5 or it may be just short of the entry point for a PR7.

The chart that follows shows the range for each PR value. It 
also shows how much PR value or PR points a page with 50 outbound 
links will pass depending on of its own PR rank. From this I have 
calculated the number of links required from each value of 
PageRank necessary for a page to attain a desired page rank.

Here is a PageRank Calculation Chart: 
(http://www.sitepronews.com/pagerank.html).

The Assumptions And The Mathematics:

For those who are interested I have used logarithmic values of 
base 5.5. In other words the value range for a PR1 lies between 
5.5 to the power of 1 and 5.5 to the power of 1.99, and PR2 lies 
between the value of 5.5 to the power of 2 and 5.5 to the power 
of 2.99 etc. The rest of the chart is fairly straight forward. 
It assumes that there are 50 links per page and that 85% of the 
PR value is passed to the recipient page.

The number of links required to attain any ranking is based on 
the median value of the donor page and the entry threshold of 
the desired PR value. In other words to achieve a PR5 you need 
5,033 points and the average points available from a PR6 page 
with 50 links is 1507.

The chart was calculated with an Excel spreadsheet and it can 
be downloaded if anyone wants to play with the calculations and 
assumptions. It might be interesting to work with a different 
base number for the logarithmic calculation. And it is also 
interesting to see the impact of more or less outbound links 
from a page.

Are These Findings Valid?

Nobody knows for sure how Google calculates PR. I have shown 
this chart to a number of knowledgeable people and they have all 
agreed that my calculations look reasonable. One SEO guru from a 
major firm said the results were very similar to independent 
research that his firm had conducted.

So take it or leave it. It is probably a fair reflection of how 
PR is passed and accumulated.

The lesson that can be drawn from this explanation and chart is 
that if you want to increase your PR you need a few links from 
pages with equivalent or higher PR, or a great many links from 
sites with lower PR.

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Bob Wakfer is the owner of Computer Partners and a long time 
student and practitioner of SEO. Computer Partners offers web 
site design, hosting and search engine optimization for its 
clients. If you would like to discuss any of these services 
with Bob you can email him at bob@compar.com.
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