Page Rating (PR) shows the strength of URL's overall internal and external backlink profile. It is measured on a logarithmic scale from 1 to 100, with the latter being the strongest.
To calculate PR, we consider:
The higher the PR of a page, the more “link juice” is transferred out to linked URLs.
The target URL splits its rating equally amongst the URLs it links to. So: a PR-10 URL which links to three other URLs can provide more "link juice" than a PR-80 URL which links to hundreds of other URLs.
Through repeated calculation, we get a PR rating for each URL. The final PR value is then obtained by scaling a computed, absolute value into the 0-100 range.
Tip: Think of PR as a relative term in the sense that it's dependent on not only the number of high-PR URLs that link to you, but also on how many other URLs these high-PR URLs link to.
Do note that it is necessary for the Site Audit crawl to be completed first in order to get accurate PR as PR is only computed after post-processing.