Cost per mille, usually written as CPM, is the price an advertiser pays for 1,000 ad impressions. “Mille” means thousand. If a campaign has a $12 CPM, you pay $12 every time your ad is shown 1,000 times, whether users click or not.
How CPM works in paid media
CPM is an impression-based pricing model used across display, video, programmatic, connected TV, and some social campaigns. The formula is simple: CPM = total ad spend ÷ total impressions × 1,000.
If you spend $600 and generate 50,000 impressions, your CPM is $12. This tells you how efficiently you are buying visibility, not traffic or conversions. That distinction matters. A low CPM can help you scale reach, but it does not automatically mean strong business performance.
Why CPM matters for search and growth teams
CPM matters because it helps marketers evaluate awareness costs, compare media buys, and forecast budget requirements before launch. For brands running search alongside display or video, CPM gives a top-of-funnel benchmark that supports fuller campaign planning.
At SEMRocket, CPM is most useful when paired with downstream metrics such as click-through rate, cost per click, conversion rate, cost per acquisition, and revenue per landing page session. That combination shows whether cheap impressions are actually producing qualified demand.
For example, a campaign with a $7 CPM may look efficient, but if the audience is poorly targeted and the landing page underperforms, total acquisition costs can still be too high. On the other hand, a $20 CPM aimed at a high-intent audience may drive stronger assisted conversions and better branded search lift.
Practical example: calculating CPM and judging quality
A SaaS company launches a display campaign to support a new keyword cluster and landing page rollout. It spends $2,400 and receives 300,000 impressions.
CPM = $2,400 ÷ 300,000 × 1,000 = $8
An $8 CPM is competitive in many markets, but the next step is what matters commercially. If the campaign also drives a healthy view-through impact, branded search growth, and assisted conversions on the targeted landing pages, that CPM is doing real work. If impressions are high but search demand, engagement, and pipeline stay flat, the media buy may be cheap but ineffective.
How to use CPM more effectively
Segment CPM by audience, placement, device, geography, and creative. Compare CPM against click quality and conversion outcomes, not in isolation. Use landing pages tightly matched to campaign intent, and track assisted performance in analytics and attribution reporting. For growth teams, CPM is best treated as a visibility cost metric that supports broader search and paid media efficiency analysis.