Online advertising can be purchased on the basis of what it costs to show the ad to one thousand viewers (CPMCPM (Cost per mille)Online advertising can be purchased on the basis of what it costs to show the…//read more ) – also called Cost per Thousand (CPT). It is used in marketing as a benchmark to calculate the relative cost of an advertising campaign or an ad message in a given medium. Rather than an absolute cost, CPM estimates the cost per 1,000 views of the ad.