CPM (Cost Per Thousand Impressions)

Cost Per Mille (CPM), also known as Cost Per Thousand Impressions, is a metric telling you how much it costs you on average to display your ads to 1,000 times.

It's calculated by adding up the cost of each user reached, divided by the number of impressions you've got.

It's closely related to the bidding system used by platforms.

CPM = (Total Cost of Campaign / Total Impressions) * 1000

It used to be the main billing method for traditional newspaper, where you paid a flat fee to get your ad printed in X thousand copies of newspapers