Adsense is one thing I've never really tried very hard to earn from but from what I understand, Adsense page impressions are counted by the number of times the ads are triggered. This month, between all of my sites, I've had 60k+ page views and 20k+ visitors, but only 1400 page impressions. From my understanding, 3 ads on a page would mean 3 page impressions when the ads are displayed. I guess I don't understand why there is such an incredible gap between the number of times the ads were shown and the number of page impressions counted by Google. Can anyone explain this to me?
maybe no ads display or public service ads was display for visitor from certain country Check your visitor, is it more than 80% of the visitor is from one country
if more than 1 ad display on same page, its 1 impression (only impressed once from visitor point of view)
you should have at least 20k+ ad impressions. If not it means, yes they didn't have enough ads for your content, or you didn't have ads on all your pages, without knowing it.
It's public service ads. To track this, try to replace public service ad with your own ads. You'll see how many visitors view your custom ads.
Adsense counts only the load of the first banner code on a page as Page Impression, that is why sometimes your page impressions are much lower then your actual clicks. Read this: Adsense Stats discrepancies explained: Clicks > PIs