. Click through rate, for the purpose of AdSense, is the number of clicks received by an ad unit divided by the total number of ad unit impressions for that ad unit. So, a better CTR can mean more revenue for you. Effective CPM: It is calculated as the cost per 1000 impressions. However, do not confuse effective CPM with your earnings. In fact, effective CPM is calculated by dividing your earnings by the number of page impressions and then multiplying the final figure by 1000. Effective CPM is generally used to compare various channels and determine which channels are more profitable for you.