There is a real complicated maths equasion I could show you about PR, but in short:-
Do you know what google page rank means and how is it calculated?
See above, it is the mathematical value of a page. Google have 2 sides to their algotithm
1. Relevance- this is textual and is language based
2. Importance - this is purely numerical,and it is this which is page rank.
In short, it is calculated whereby a page can 'vote' an amount up to 85% (approx) of its own PR value for that page. The value is set, then shared out across all the links on that page, internal and external follow and nofollow. (Nofollow share gets lost as it is blocked from passing juice). The amount per link is not equal though, as a link in the body copy of your page would get a higher value than a footer link for example.
I know the page rank start from 0 the worst up to 10 the best ranking.
Well there you go, it is higher than 10 though it just doesn't display on the toolbar
What google page rank a website should have to be considered as doing all right.
Forget about PR, get links for traffic, and build your site as well as you can. PR will follow.