CPM or CPI  is frequently used measurement in advertising. CPI or Cost Per Impression is the cost incurred for each prospective customer who views the advertisement, whereas CPM (Cost Per Mile) alternatively known as Cost Per Thousand (CPT) refers to the cost incurred for every thousand prospective customers who view the advertisement. For one thousand views or clicks of an advertisement, advertiser pays this cost. 

How CPM is Calculated?

Divide the total number of impressions the ad will make by 1,000. For instance, if your ad would make 10,00,00 impressions, you would divide 10,000 by 1,000 to get 100.