What is CPM?

CPM — cost per mille — is what a thousand ad deliveries cost: spend divided by impressions, times 1,000. It is the purest price of attention a platform charges you, before your creative or landing page has any say.

Formula

CPM = ad spend ÷ impressions × 1000

Worked example

A channel spends €4,500 to serve 300,000 impressions: CPM is €4,500 ÷ 300,000 × 1000 = €15. If next month the same €4,500 buys only 250,000 impressions, CPM has risen to €18 — a 20% price increase in the auction, even if clicks and sales look unchanged so far.

How Saldo Metrics computes it

v_channel_performance computes cpm_base per channel per day as summed spend_base over summed impressions, scaled by 1,000; the channel summary on Marketing → Overview recomputes the division across the selected period, and v_channel_summary carries the lifetime avg_cpm_base. The CPM trend dashboard widget groups the same view by month — total monthly spend over total monthly impressions — so each point is a volume-weighted price, not an average of daily rates. Spend is EUR, converted per day at the ECB rate before any summing.

Why it matters

CPM is the input cost every other efficiency metric inherits. When true ROAS drops, the first diagnostic question is whether attention got more expensive (CPM up), the ads got less clickable (CTR down), or the site converted worse — three different fixes. The monthly trend widget isolates the first factor, and a CPM spike is one of the anomaly types the anomaly monitor flags.

Common mistakes

• Reading seasonal CPM inflation as a performance problem. Auction prices rise every Q4 across the board; compare against the same month last year, not last month.
• Comparing CPM across placements or formats as one number. Video and feed inventory are priced differently by construction.
• Optimizing CPM down without watching who the cheap impressions reach. The cheapest audiences are often cheap because nobody wants them.

Where you see this in the app

Marketing → Overview, in the channel summary table's CPM column; the Channel CPM Trend dashboard widget; and CPM-spike alerts in the anomaly monitor.