The ad request click-through rate (CTR) is the number of ad clicks divided by the number of ad requests.
Ad request CTR = Clicks / Ad requests
For example, if you received seven clicks out of 1000 ad requests, then your ad request CTR would be 0.7%. (7 / 1000 = 0.7%)
Note: This metric is only available under the 'Advanced' metric family tab. Learn more about picking metrics for your report.