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CPM (cost per mille): definition

Paid advertising

By Alvyn Detavernier, founder · published October 28, 2026

Definition

CPM (cost per mille) is the price an advertiser pays for 1,000 impressions of an ad, whether or not anyone clicks. It is calculated as CPM = cost ÷ impressions × 1,000. In Google Ads, viewable CPM (vCPM) bidding only charges for impressions that actually had a chance to be seen on screen.

Also known as: cost per thousand impressions, vCPM, viewable CPM

The formula and converting to CPC

Formula: CPM = total cost ÷ impressions × 1,000. CPM links directly to cost per click through click-through rate: CPC = CPM ÷ (1,000 × CTR). With a $10 CPM and a 0.5% CTR, each click costs $10 ÷ 5 = $2. That conversion lets you compare a campaign bought on impressions with one bought on clicks. To plan a budget, run it backwards: impressions = budget ÷ CPM × 1,000.

CPM and viewable CPM in Google Ads

Google Ads offers CPM bidding on the Display Network, plus viewable CPM (vCPM), which only charges for viewable impressions. A display impression counts as viewable when at least 50% of the ad's area is on screen for at least one second; for video, at least two seconds. Existing CPM bids are automatically converted to vCPM, but Google recommends revisiting them, since viewable impressions are worth more.

When to buy on CPM

CPM fits awareness goals: launching a brand, opening a new location, promoting a local event, running a YouTube video campaign. On social platforms such as Meta and LinkedIn, it is also the standard measure of what reach costs, even when delivery is optimized for conversions. When the goal is leads or sales, judge the campaign on cost per acquisition instead. Either way, pair CPM buying with tight targeting and a frequency cap, or a small budget burns through the same few thousand people.

The traps of cheap impressions

Low-quality placements: mobile apps and games that generate accidental clicks.
Excessive frequency: the same person sees the ad fifteen times a week.
Real viewability: a banner at the bottom of a page nobody scrolls to costs money and returns nothing.
Context: review where your ads appear and exclude sites that could hurt your brand.

Example

Example: a restaurant opening in San Diego puts $800 into a local video campaign at an $8 CPM, buying 100,000 impressions. With an average frequency of 4, the ad reaches about 25,000 people within five miles, roughly 3 cents per person reached.

Sources

Cost-per-thousand impressions (CPM): Definition, Google Ads Help
Understanding viewability and Active View reporting metrics, Google Ads Help

Frequently asked questions.

What is a good CPM?

There is no universal benchmark: CPM varies by platform, format, audience, season and competition. A low CPM is not good if it buys poorly viewable or badly targeted impressions. Compare your own campaigns against each other and always tie CPM back to the cost of the result you want.

Should I choose CPM or CPC bidding?

Choose CPM when the goal is to be seen by a specific audience, such as for a launch or an event, and CPC or conversion-based bidding when you want clicks or leads. On Google's Search Network, pay per click remains the norm; CPM mainly applies to display and video.

Related terms.

The concepts that go with it, to round out the definition.

Paid advertising

CPC (cost per click)

CPC (cost per click) is the amount an advertiser pays each time someone clicks on their ad. Max CPC is the highest bid you are willing to pay, while...

Paid advertising

CPA (cost per acquisition)

CPA (cost per acquisition) is the average amount of ad spend needed to generate one conversion, such as a sale, a quote request, a booked call or a...

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