Sunday, April 29, 2007

Google PageRank Formula

Forumla

0.15 + 0.85 x ( a share of the PR of every webpage that links to it) = Your Webpage PR




0.15 = The lowest PR a webpage could ever possibly have.

0.85 = A dampening factor... This is just the number that Google uses for their PR formula.

"share" = the PR of the page linking to you divided by the total number of links on that page.

Example:

Say we've created our website and it has 3 pages in total. For sake of making the math easy,
we'll start each webpage with a page rank of 1.
  • Page A
  • Page B
  • Page C

None of the pages link to each other. They're just pure content webpages with no links to any
other pages within our website. Let's quickly calculate the PR of our pages by using the formula
above.

0.15 + (0.85 x 0 ) = .15

Because no webpages link to our pages, there is no "share of PR"... hence it is 0.
So... If we do the math, we come up with a PR of .15 for each of our pages.

Now, let's see what happens if we link page A to page B.


Using our formula we get:

  • Page A : 0.15 + (.85 x 0) = .15
  • Page B : 0.15 + (.85 x 1/1) = 1
  • Page C : 0.15 + (.85 x 0) = .15
You can see that by just linking page A to page B, we've changed the PR of page B from .15
all the way up to 1. Big difference!
With our newly calculated Page Ranks for all of our pages, let's do the calculation again. By
doing so, we'll slowly get to the "true page rank" of all of our pages... The more iterations we
do, the more gradual the change will be between each iteration.

  • Page A : 0.15 + (.85 x 0) = .15
  • Page B : 0.15 + (.85 x .15/1) = .2775
  • Page C : 0.15 + (.85 x 0) = .15
You can see that after another iteration of our formula, the PR of page B dropped
significantly... This number is closer to the actual Page Rank that Google would give page B.

Now, let's try something different and link all pages to and from one another...



  • Page A : 0.15 + (.85 x 1/2) = 5.75
  • Page B : 0.15 + (.85 x 1/2) = 5.75
  • Page C : 0.15 + (.85 x 1/2) = 5.75
After 1 iteration the Page Rank of all pages is .575.
So, by linking ALL pages together we have maximized the page rank from within our website!
You can play around with your linking throughout your website and by doing so, you can send
more PR to pages you want to rank higher for, and lowering the PR of those pages you don't
care much about their ranking :-)
This can be extremely powerful.

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