Achieve Web Site Design & Internet Marketing: Google Page Rank & How It Works

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).

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.

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.

Page Rank Calculation

PR	Start	End	Median	Median	Links	Links	Links	Links
PR	Range	Range	Value	PR Passed	for PR5	for PR6	for PR7	for PR8

1	6	30	18	0.30	16,803	92,414	508,277	2,795,522
2	30	164	97	1.65	3,055	16,803	92,414	508,277
3	166	900	533	9.06	555	3,055	16,803	92,414
4	915	4,948	2,931	49.83	101	555	3,055	16,803
5	5,033	27,213	16,123	274	18.362	101	555	3,055
6	27,681	149,670	88,675	1,507	3.339	18.362	100.992	555.456
7	152,244	823,186	487,715	8,291	0.607	3.339	18.362	100.992
8	837,339	4,527,522	2,682,431	45,601	0.110	0.607	3.339	18.362
9	4,605,367	24,901,372	14,753,369	250,807	0.0201	0.110	0.607	3.339
10	25,329,516	136,957,543	81,143,530	1,379,440	0.0036	0.020	0.110	0.607

Assumption: 85% of median value passed
Assumption: 50 links per page average

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.

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.

Web Design Denver

Google PageRank and How To Get It