PageRank is a log scale, not a linear scale.

If it were a linear scale, a PageRank of 5 would be simply 25% more valuable than a PageRank of 4, but in reality, a PageRank of 5 is approximately 5x the value of a PageRank of 4. So too is a PageRank of 8 about 5x the value of a PageRank of 7.

Google sets the value of all these PageRanks, and the exact formula is a well-guarded secret. In addition, they refine and modify the formula regularly. They store the calculated PageRanks of all indexed pages on the web somewhere in one of their databases.

PageRank value increases approximately 5x for every integer increase in PageRank.

Let's say your PageRank was 3. As you look at the New York Times home page, with a PageRank of 9, you could be forgiven for thinking that the NY Times home page PageRank was 3 times the value of your PageRank. In actuality, the NY Times home page PageRank is worth tens of thousands of times more.

A PageRank of 5 is actually "five-point something", not necessarily 5.00; it could be 5.04 or 5.98. I don't know how many decimal places Google holds for every PageRank it stores, but one or two decimal places would be enough - 5.22 or 5.2 is as meaningful as 5.22363292 - the number is an approximation to begin with.

Tags: PageRank, SEO