CPM Calculator

One formula, three unknowns

The ×1,000 is the step people forget. Cost per single impression here is $0.0075, which is too small a number to compare comfortably, so the industry quotes it per thousand.

What counts as an impression

An impression is not a person and not a guaranteed view. Under the MRC and IAB desktop display measurement guidelines, an ad impression is counted when the ad has loaded and at minimum begun to render on the user's device; it does not require any portion of the ad to be visible on screen. The guidelines also reject server-side "count on decision" methods, because they are the furthest from the user actually seeing the ad.

Because a rendered ad can still sit below the fold, the MRC defines a stricter viewable impression:

That gives a second price, vCPM (cost per thousand viewable impressions): cost ÷ viewable impressions × 1,000, or simply CPM ÷ viewability rate. A $7.50 CPM with 60% viewability is a $12.50 vCPM. When comparing vendors, compare them on the same basis: served CPM against served CPM, or vCPM against vCPM.

CPM, CPC, CPA and CTR: converting between them

Advertisers buy on one metric and judge results on another, so it helps to move between them.

A $5 CPM costs very different amounts per click depending on how often people click:

Clicks have their own counting rules. The IAB Click Measurement Guidelines treat clicks as a media-buying currency with their own filtration requirements, and note that some counting methods allow several clicks per impression, which can even produce click-through rates above 100%. When a CPC campaign and a CPM campaign are compared, both should use filtered, comparable counts.

eCPM and RPM on the publisher side

Publishers run the same formula from the other direction. eCPM for a placement is revenue ÷ impressions × 1,000, which lets a site compare CPM, CPC and flat-fee deals on one scale. RPM (revenue per mille) usually means revenue per 1,000 page views rather than per 1,000 ad impressions; a page carrying three ads earns roughly three ad impressions per page view, so its RPM can be several times its eCPM.

Why CPMs differ so much

There is no single "good CPM", and benchmark figures quoted without context are not reliable. CPM moves with audience targeting (narrow audiences cost more per thousand), format (video usually costs more than static display), placement and viewability, auction competition and season, and with whether fees are included. A fair comparison holds those constant: same geography, same format, same viewability standard, and costs either all gross or all net of agency and platform fees.

Planning a campaign backward from a goal

The same formula sizes a budget before launch. Start from the outcome and work back through the funnel:

• Target conversions → clicks: 50 bookings at a 4% conversion rate need 50 ÷ 0.04 = 1,250 clicks.
• Clicks → impressions: at a 0.25% CTR, 1,250 clicks need 1,250 ÷ 0.0025 = 500,000 impressions.
• Impressions → budget: at a $7.50 CPM, 500,000 impressions cost 7.50 × 500,000 ÷ 1,000 = $3,750 (use the "Cost" mode).

Each step multiplies the uncertainty of the one before it, so run the numbers with a pessimistic and an optimistic CTR. If the goal is reach rather than conversions, divide the target number of people by the planned frequency instead: reaching 100,000 people three times each needs 300,000 impressions.

Common CPM mistakes

• Treating impressions as people. Reach is impressions ÷ average frequency: 320,000 impressions at a frequency of 4 is about 80,000 people.
• Comparing served CPM with viewable CPM. A cheap CPM with low viewability can cost more per viewable impression than a pricier one.
• Judging a performance campaign by CPM alone. If the goal is sales, convert to CPA; a higher CPM with a better conversion rate can be the cheaper buy.
• Dropping the ×1,000. $2,400 ÷ 320,000 = 0.0075 is the cost per impression, not the CPM.