A pageview of an article is priced differently than a frontpage. You probably also have pages on your site, that dont show ads at all. So first, you need to consider what pages you want to measure. Typical a frontpage contains more ads and have a higher price per page view than other pages. If you want to measure individual page types/templates, you need to be able to cluster these together in your analytics. Your taxonomy may be the key to this, where you search landingpages starting with 'www.mydomain.com/articles', and know that all articles show 5 ads per page. Doing this enables you to get a better indication of cost rather than just on how many pageviews you lose revenue. We assume you already have statistics running on your site, like Google Analytics or similar. If not, get that up and running first!
As VisuAD only supports Google Doubleclick for Publishers at this time, we describe the method using this. You need to create a new Adunit for measuring Adblockers. It will be invisible on your site, but make sure it cant be used for anything else in your setup of DfP, by setting it as a 'Special ad unit'. The available size on the adunit should be 1x1 pixel. Make an Adunit for each pagetype you want to track (see 1), and implement the code on the templates.
Prepare a transparent 1x1 PNG, called 'AD.png' and create a new order running on each of the new adunits. They should run indefinitely. When it is running reload your page, and make sure it is delivered on the page(s) you're measuring. Identify it in code. Next install an adblocker and confirm that it blocks the adunit. An adblocker usually add CSS-code to the adunit, like 'Display: none'. If you're unsure if it does, you could try making the creative in a strong different color visible to you on the site, so you can visually confirm that the adunit gets blocked. When you have confirmed it gets blocked, you could replace the creative again with the transparent version.
With the Adblocker installed, you also need to confirm that a page load does'nt count as an impression in DfP. Test this on a page that is unavailable for the public, gets very few pageviews or create a new page for it. Loading the page with an adblocker should not increment the number of impressions. This may take a few days to test as DfP is'nt always as realtime as we would wish. This is not failsafe: Some Adblockers may in fact still count as an impression even if the ad is not shown on the page.
If all above is in place, you can now compare the number of pageviews with the number of impressions of the Adunit(s). The difference between the two is the number of adblocked pages. If a page contains more adunits, you should multiply the number with the number of adunits and this number you can use with your CPM to calculate the amount of lost revenue on your site. If you segmented your pagetypes, you will get a very good indication of how much revenue you're losing.
This method will only give you an indication, and is not a 100% precise calculation, as Adblockers work in mysterious ways to bypass your site. If you do not have a fallback integration of the adunit, using 'Simplified URL tags', you may end up counting users with javascript disabled as adblock-users aswell - they are in fact not (either way, you don't get ads shown to them). We also know some adblockers may still count as impressions in DfP. It is very dependant on how your site is coded in the frontend. VisuAD gives you a much more precise calculation when running it on your site, but this method may provide you with data that support your decision on fighting back against the Adblocker phenomenon.
If you want our help on analyzing the impact of Adblockers on your site, please contact us.