What is CPM? Cost Per Mille Explained
Short answer: CPM (cost per mille) is how much you pay per 1,000 ad impressions. CPM = (total spend ÷ impressions) × 1,000. A $10 CPM means you pay $10 every time your ad is shown 1,000 times, regardless of clicks.
CPM formula
- CPM = (total spend ÷ impressions) × 1,000
- Example: $100 spend on 50,000 impressions = $2.00 CPM
- To find total spend: Spend = (CPM × impressions) ÷ 1,000
- To find impressions: Impressions = (spend ÷ CPM) × 1,000
What counts as an impression?
An impression is counted each time your ad is displayed. Most platforms record it when the ad loads. Some — including Facebook — use a “viewable impression” standard, requiring the ad to be at least 50% visible for at least one second.
One person can generate multiple impressions. Showing the same ad to the same person three times = 3 impressions, 1 unique viewer. The ratio of impressions to unique viewers is called frequency.
CPM vs CPC vs CPA
- CPM — pay per 1,000 impressions. Best for reach and brand awareness.
- CPC — pay per click. Best for traffic-focused campaigns. See what is CPC.
- CPA — pay per conversion or set a target cost per acquisition. Best for direct-response. See what is CPA.
You can convert between them: if CPM is $10 and CTR is 2%, your effective CPC is $0.50 (10 ÷ 20 = 0.50). Understanding all three helps you compare costs across campaigns and channels.
When to use CPM bidding
- Brand awareness — maximise reach at the lowest cost per view
- Retargeting warm audiences — stay visible to people who have already visited your site
- Video and display campaigns — where impressions and views are the primary KPI
For campaigns focused on sales or leads, CPC or target CPA bidding typically delivers better return because you only pay when someone takes action.
What drives CPM up or down?
- Audience specificity — Narrow, high-value audiences (e.g., LinkedIn by job title) carry higher CPMs
- Ad placement — Premium placements (Facebook Feed, YouTube pre-roll) cost more than lower-visibility slots
- Competition / seasonality — CPMs spike sharply in Q4 as more advertisers compete for the same impressions
- Ad quality and relevance — Poor engagement rates on social platforms raise effective CPM
- Industry — Finance, legal, and insurance verticals consistently produce the highest CPMs
Common mistakes
- Using CPM for conversion campaigns. If you want sales, optimise for ROAS or CPA — not impressions.
- Ignoring frequency. A low CPM with high frequency means you’re repeatedly showing the same ad to the same people, wasting budget and causing fatigue.
- Comparing CPM across channels without context. A $50 CPM on LinkedIn reaching CFOs may generate more pipeline than a $3 CPM on broad display. See what is a good CPM for channel benchmarks.
FAQ
What is a good CPM?
It depends on the channel. Google Display: $2–$5. Facebook/Meta: $5–$15. LinkedIn: $30–$100+. See what is a good CPM for a full channel breakdown.
Is CPM the same as eCPM?
Not exactly. eCPM (effective CPM) normalises revenue or cost across different pricing models to a per-1,000-impressions figure, making it easier to compare. CPM is your actual buy price.
How do I lower my CPM?
Broaden your audience, test lower-cost placements, improve creative engagement (higher engagement lowers effective CPM on social), and avoid peak competitive seasons when possible.