What do you get when you divide total cost by the total number of served impressions and multiply by 1000?

When you divide total cost by the total number of served impressions and multiply by 1000, you are calculating the Effective Cost Per Mille (eCPM). This metric provides a standardized way to evaluate the cost of advertising per 1,000 impressions, making it easier for advertisers to compare the performance of different campaigns or ad placements.

By multiplying the result by 1000, you convert the cost per impression into a metric that reflects how much an advertiser pays for every thousand times their ad is shown. This is particularly useful in digital marketing, as it helps advertisers assess the efficiency and effectiveness of their media spending compared to industry benchmarks or other campaigns.

Considering the context of the other options: Cost per click specifically measures the cost for each click on an ad, the click-through rate assesses the ratio of clicks to impressions indicating ad relevance, and return on advertising spend calculates the revenue generated per dollar spent on advertising. These metrics serve different purposes and are not interchangeable with eCPM.