The percentage of impressions that were viewable out of all measurable impressions. This metric only includes impressions from regular AdSense for content, AdSense for video and AdSense for games ad units, it doesn't include data from link units, or data from dynamic allocation in Google Ad Manager. Learn more
All viewable ads are measurable, because you can't confirm that an ad has met the criteria for viewability unless it can be measured. For example, say the ads on your site had 100 measurable impressions. That means there were 100 impressions where Active View tags were able to measure viewability. If only 10 of those 100 impressions were measured as viewable, then the site would have 10% Active View Viewability.