Cost Per Thousand Impressions "A.K.A Cost Per Mille" is an advertising metric. It refers to how much you pay per 1,000 impressions (‘mille’ means 1,000 in Latin). If your goal is to get your ad in front of as many eyes as possible and spread brand awareness, CPM is an important metric to follow. Like CPC, CPM varies based on your targeting options and the quality of your ad.