The simple answer is: PR is calculated on a page by page basis dependent only on the cumulative effect of the total amount of PR passed to that page by the links pointing to it. The PR shown by the tool bar (fool bar) is only an estimation and not the actual PR of a given page.

There are lots of factors to calculate the pagerank and one of the major factor is the backlink.

If by "pagerank" your mean how high you rank in the index for any given term, then yes you are correct.

If by "pagerank" you mean PR, then there is only one factor. Whatever PR any page has is determined by the cumulative amount of PR being passed to that page through links on other pages pointed to that page.

Just wanted to make sure that we were all on the same "page".

Its not just back links but the amount of Quality of back links that you are getting.. Google gives more value on the quality of back links that you are getting compared to those irrelevant sites..

It also depends on the life age of your website and the relavance of your content.

Sorry. That's absolutely incorrect. PR has nothing to do with the relevance of your content or the age of your domain.

interesting what you are saying here. i did not know that PR had nothing to do with the relevancy of your content and the age of your website. i thought it would, simply because some old websites, many of them long abandoned by their webmasters, seem to maintain high PRs. but it can be due to other factors as well.

The misconception that some older web sites have higher PR is simply because they have had more time to accumulate more inbound links, not because they have more relevant or better quality content. PR is all about links. That's it.

You are incorrect, these do play a factor.

What's the number 1 thing that you need in order to be indexed by Google, CONTENT. If you have a site that has 100,000 backlinks but has no quality content, it will not achieve a high PR.

Also, if you have a site that is 1 month old and achieves 100,000 backlinks, You will not all the suddent have a PR 10

The reason for this is if you very quickly achieve a large amount of backlinks Google will believe that you are gaming the system and will disregard your links. Review the "manipulating links" section on Wikipedia.

This also explains why a site moves up gradulally PR 1, then PR 2, then PR 3 and doesn't jump from PR 1 to PR 8 between updates.

These things all play a factor whether or not you realize it. Believe me, I've done my homework.

Sorry. I don't know what type of homework you have done but I can assure you that content has nothing to do with PR.

Wrong again. I have seen many "garbage" sites with a PR of 5 or 6. Granted they may not retain the high PR long because they were artificially attained in the first place and the high PR links that got them there were busted down. But it really is all about backlinks. Again: The PR attained by any page is the direct result of the cumulative amount of PR being passed to that page by links from other pages. Here's a link that will allow you to do some valid "homework". http://www.webworkshop.net/pagerank.html