CPM

What it is

CPM (Cost Per Mille) is the cost an advertiser pays for 1,000 impressions of an ad. "Mille" is Latin for thousand. An impression is counted each time an ad is served or rendered, regardless of whether anyone clicks or converts.

The formula is simple:

• CPM = (Total Spend / Impressions) x 1,000

Or, rearranged to forecast spend:

• Spend = CPM x (Impressions / 1,000)

Why it matters

CPM is the standard currency for awareness and reach campaigns, where the goal is to put a message in front of as many relevant people as possible rather than to drive an immediate action.

• It normalizes cost across channels and formats so you can compare display, video, social, and out of home on a common basis.
• It is the native pricing model of most programmatic and reservation buying, including brand campaigns.
• It separates media cost from performance, which is useful when the value of an impression is upstream (recall, consideration) rather than a direct click.

CPM says nothing about quality on its own. A low CPM with poor viewability or bot traffic can cost more per real human view than a higher, cleaner CPM. This is why practitioners pair it with viewability, frequency, and vCPM (cost per viewable thousand).

How it is used in practice

• Planning: estimate reach for a fixed budget, or budget for a target reach.
• Benchmarking: compare inventory sources, placements, and audiences.
• Buying: set bid caps in auctions, or negotiate fixed CPM deals.
• Bridging metrics: combine with CTR to derive CPC, or with conversion rate to derive CPA.

Related conversions:

• CPC = CPM / (CTR x 1,000)
• Effective CPM (eCPM) restates any pricing model (CPC, CPA) back into a per thousand impression cost for comparison.

Worked example

You run a brand awareness campaign with a 10,000 EUR budget at a negotiated CPM of 8 EUR.

• Impressions = (Budget / CPM) x 1,000 = (10,000 / 8) x 1,000 = 1,250,000 impressions.
• If the average frequency target is 5, unique reach is roughly 1,250,000 / 5 = 250,000 people.
• If CTR is 0.4 percent, clicks = 1,250,000 x 0.004 = 5,000, so CPC = 10,000 / 5,000 = 2 EUR.

Same impressions at a 12 EUR CPM would cost 15,000 EUR, a 50 percent increase in media cost for identical delivery, which is why CPM discipline directly protects margin.