Nobody, other than a few people at Google, knows exactly. Based on observation and analysis, we can make some assumptions.
It seems that PageRank is assigned according to a logarithmic calculation. It also seems that you need between 8 and 10 PageRank 1 sites to link to your site for you to have a PageRank of 1. Let us assume it is 8. The following is then a possible scenario:
To Have |
You need |
PR 1 |
8 PR 1 Links (8¹) |
PR 2 |
64 PR 1 Links (8²) |
PR 3 |
512 PR 1 Links (8³) |
PR 4 |
4,096 PR 1 Links, etc |
If this was true, then you would also see that one PR 3 link could result in a PageRank of 1, or one PR 5 link in a PageRank of 3.
There are however other factors that we know play a role. If there are only one link coming off the PR 5 page, then the above may be true. However, if there are multiple links coming off the same page, then the PageRank seems to be divided by the number of links.
I trust that this was enough to convince you that we don't really know!
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