Cost Per Mille (CPM)

What CPM actually means

CPM is the price of attention before anything happens with it. It is an input cost rather than a performance metric, which is exactly why it belongs in a board conversation about efficiency: when CAC rises, CPM inflation is one of the few explanations entirely outside the company's control. Auction-based platforms price by demand, so CPMs climb in competitive quarters no matter how good the marketing is.

Worked example

A campaign spends 18,000 dollars and serves 3,000,000 impressions, so CPM is 6 dollars. If the same audience costs 9 dollars in the fourth quarter, the team needs a 50 percent improvement in conversion rate just to hold CAC flat.

Why the board cares

When a marketing leader has to explain rising CAC, separating CPM inflation from execution decline is the difference between a market problem and a management problem. Boards accept the first and act on the second, so that split needs to be in the deck before anyone asks for it.

Common mistakes

• Reading a low CPM as efficiency when it usually indicates low-quality or low-intent placements.
• Comparing CPMs across formats and platforms as though a video impression and a display impression are the same unit.
• Failing to separate CPM inflation from conversion decline when explaining a CAC increase.

Related terms

• Cost Per Click (CPC)
• Cost Per Acquisition (CPA)
• Return on Ad Spend (ROAS)
• Marketing Efficiency Ratio (MER)

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