Newbie Adsense publishers are sometimes puzzled when their Google Adsense page impressions are different from the pageviews reported by web stats software like SiteMeter, Statcounter or Google Analytics.

First things first. The page impressions column in Adsense stats shows how many times a webpage containing Adsense ads was viewed by a visitor. Even if your webpages have multiple ad units, they'll will still account for a single page impression per page view in Adsense reports.

Adsense Page Impressions
There are several reasons why the hit count (or page views) reported by Adsense is lower than the numbers displayed by your stats package:

1. Users may have installed ad-blocking software (like AdBlock plus) or have modified their Windows hosts file to block their computer from downloading Adsense scripts. In either of the cases, Adsense Javascripts won't be executed though your site stats script will still register a page impression.

2. Adsense doesn't have enough ad inventory for your page. In such a situation, Google will show alternate ads or fill the area with custom colors but won't increment the page impression count.

3. Site visitors are viewing the webpage inside a browser like Lynx (which won't run Javascripts) or older browser versions that don't support IFRAME or their sys admins have disabled Javascript due to security reasons. Adsense ads won't appear in either case but the stats software may still count an impression via the <noscript> tag.

4. It is possible that the default timezone of your stats software is different from Adsense which works according to the US Pacific Time. If that's the case, there will always be a mismatch between the two figures.

5. If a website is slow or a particular webpage is heavy on graphics and widgets, users sometimes abort loading the webpage by pressing the escape key. This may lead to lower Adsense page impressions because the Adsense ads that are located later in the HTML code may not load.

There's little you can do here to match the numbers since it mostly depends on the settings of visitors' web browser and Adwords inventory. However, you may change your stats software default timezome to match that of Adsense (Pacific Time).