PageRank is a formula that assigns a value to every page in the Google index. Google displays search results based on an algorithm which includes the value of PageRank. So the higher your site's PageRank, the more likely it is that you will receive a top listing on the search result page when someone types in the keywords for your site.
It's very simple to see anyone's PageRank. Just download and install the Google toolbar. It's a very quick and easy install. Just be sure to choose the Advanced option during the install so the PageRank of each site you visit will be displayed on the toolbar.
The formula appears so complex you would probably have to be a mathematician to even have a chance to decipher it anyway. It looks something like this:
PR(A) = (1-d) + d(PR(t1)/C(t1) + ... + PR(tn)/C(tn))
Basically PageRank formula works like this. The more links that point to your website the higher your PageRank will be. The higher the PageRank of the referring page that has your link on it, the more PageRank you receive from Google. For every outgoing link that a page has, the value of those links drop. So for example, a link from a page with a PageRank of 4, and only 3 other links, is worth more than a page with a PageRank of 5 and 100 links. It is also believed that Google assigns more value to a link that comes from a site with similar content. So as you can see, there are many variables when calculating PageRank.
PageRank can be increased by the number of incoming links to your website from other sites on the Internet. In addition, it requires anywhere from five to seven times more to get from one level of PageRank to the next.
So for example, (and this is not a true formula) if 100 PageRank 3 sites with a link to your page give you a PageRank of 4, then it would take around 500 more PageRank 3 sites to link to you before you became PageRank 5. However if you had 1 link from a PageRank 8 site, that might be enough to give a higher PageRank all by its self. It's really all relative and trying to figure it out will simply drive you mad, so don't bother. :) The best thing you can do is obtain as many quality incoming links from other sites with similar content as you possibly can.
Another important factor is the number of pages on your site. The more pages on your site, the higher potential you have to gain in PageRank. More pages doesn't mean you will get a higher PageRank only that you won't hit a ceiling. Apparently Google has a cut off point somewhere on the highest PageRank it will give to sites with a low number of pages.
According to the Google website, they update the index about once a month. However if you spend any amount of time reading search engine forums, you will find that results vary for every webmaster. PageRank may not update or may change drastically for a long period of time which is often times unexplainable. Usually as long as you follow good web site optimization techniques and maintain enough quality incoming links, the index will eventually assign your website PageRank and adjust any changes which may have been made in error.
By: Patrick Carlow
picture from: MarketingSqueeze