CPM, like its name suggests, allows Internet marketers to obtain a quantitative figure of how much it costs for 1000 impressions. To date, CPM is the most common technique used by marketers to assess the price of a web ad.
CPM, or cost per thousand, refers to the cost of a marketing campaign that reaches at least 1000 people. The letter “M” in the term refers to the Roman numeral for 1000.
The formula is: CPM = Cost / Impressions * 1000