I have set up Google DFP responsive ads using this method: https://support.google.com/dfp_premium/answer/3423562?hl=en Right now I have an ad unti that will show the following ads based on size: var mappingTop = googletag.sizeMapping(). addSize([990, 200], [970, 90]). addSize([748, 200], [728, 90]). addSize([488, 200], [468, 60]). addSize([320, 200], [320, 50]). build(); So there are 4 possible ad sizes that can show based on the widths defined in the first array. What I am looking for is how to get stats on each of those four ad sizes so that I can better report to advertisers what kind of inventory I have for each? For example, how do I determine how many mobile ads I am serving at the 320x50 ad size? I am looking around Google DFP and not seeing this. I can see how many total impressions that ad unit is showing, but can not break it down by size.