PageRank (PR) is the Google's view of importance of a webpage. Goolge will assign PR in the range of 0 to 10. 0 represents less importance and 10 represents more importance.
Individual PR is applicable for each webpage in a website, it is not common for whole site.
Finding PR of a webpage is very simple. Just we need to install google tool bar.
Once after installing the google tool bar, we can see the PR of any webpage loaded in our browser just by seeing progress bar in the PageRank icon in the Google toolbar. Please refer the screenshot image.