How many sites belong to Google Display AdSense network?

According to Google itself, theoretically it is possible to reach 90% of internet users through a network of 2 million websites that are members of Adsense. These numbers seem a bit inflated, but even if they were respectively 45% of users and 1 million websites it would already be quite enough. The real problem is not how many people you reach, but what you tell them once you’ve reached them.