My guess of how Google's Page Rank works

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This page describes my guess of how Google Page Rank works.

Each page has a number of page points on a scale of 0 to 4294967295 This is a 4 byte unsigned integer stored with the page data. For display purposes only, the page points are converted to PR0 to PR10+ using the scheme below, by rounding down.

PR=0 means 1 point
PR=1 means 8 points
PR=2 means 64 points
PR=3 means 512 points
PR=4 means 4092 points
PR=5 means 32736 points
PR=6 means 262144 points
PR=7 means 2097152 points
PR=8 means 16777216 points
PR=9 means 134217728 points
PR=10 means 1073741824 points
PR=10+ means 4294967295 points. (note the scale does not quite get as far as PR=11)

Transfer of PR

1. Determine the number of outgoing links on the sending page

At the sending end page, count the total number of equivalent links on the page by pretending that any bold or strong links are there twice over.

Round up the number of equivalent links to the next binary step on the binary scale:
1 2 4 8 16 32 64 128 256 512 1024 etc.

So, for example, a page with 8 regular links and 2 enhanced links counts as having 12 links and this is rounded up to 16.

2. Work out the page points to be transferred by each link as follows.

Divide the page points of the sending page, by shifting the requisite number of bits sideways. e.g. divide by 16 means 4 shifts. This is extremely fast and involves no maths.

The answer is the number of page points to be transferred per link. The number of page points transferred tends to be somewhat less than the full share because of the rounding up process for the number of links. This represents an average damping factor of about 0.25

When doing the page points transfers any bold links would have the points transferred doubled. If there were several links on the page all pointing at the same target page, each would be actioned as independent links.

Display of PR value in the Google toolbar

Google displays the PR of a page in its Google Toolbar as a short variable length green line. The information used for the display process is updated every few months. This means that recently created pages may show as having zero PR of up to three months. There is an exception to this: In the case of sub-pages whose urls have a ? followed by trailing parameters such sub pages are shown as having a PR value immediately. The value should be considered as very approximate. It is probably calculated on the fly by dividing the real PR which belongs to the root page url name (without any training parameters) by some approximation of the total number of sub-pages..

Please note that "Google", "PR" and "PageRank" are trademarks of Google.

Page last amended 8 June 2008