CPM vs CPC: What's the Difference?

CPM (Cost Per Mille) is the price paid per 1,000 impressions, regardless of whether anyone clicks. It's a reach-based pricing model - you're paying for the ad to be shown, not for a result.

CPC (Cost Per Click) is the price paid each time someone actually clicks the ad. It's an action-based pricing model - impressions with no clicks cost nothing.

Neither model is inherently cheaper; it depends on the expected click-through rate. A CPM campaign becomes expensive per click if the creative doesn't get clicked much, since you're paying for impressions that produce no action. A CPC campaign becomes expensive per impression if the click-through rate is high, since every one of those clicks is billed individually. As a rough rule: CPM tends to suit brand-awareness goals where reach itself has value regardless of clicks, while CPC tends to suit direct-response goals where the click is the thing actually being paid for. Converting between the two (CPM ÷ 1000 × expected CTR ≈ effective CPC) is a useful sanity check before assuming one bidding model is automatically the better deal.