What Is CPM in Advertising? How to Calculate Cost per Impression

CPM stands for cost per mille, Latin for "per thousand". It is the price an advertiser pays for 1,000 impressions of an ad, and it is the standard way to price and compare awareness campaigns on display networks, video, social media and programmatic platforms.

An impression is counted each time your ad is served on a screen. It doesn't matter whether anyone clicks. That is the key difference from cost per click (CPC): with CPM you pay for reach and visibility, with CPC you pay for visits.

CPM is used in two ways:

➔ As a bidding model: you agree to pay a set price per 1,000 impressions, for example with CPM or viewable CPM bidding in Google Ads.
➔ As a metric: even if you pay per click, you can calculate your effective CPM to compare the cost of reach across channels and campaigns.

The cost per impression formula is simple:

CPM = (Total cost ÷ Total impressions) × 1,000

You can rearrange the same formula to answer the other two questions advertisers usually ask:

Always use cost and impressions from the same date range and the same campaign, or the result won't mean much.

The numbers below are illustrative examples, not benchmarks, so you can see how the formula works in practice.

➔ Example 1: Find your CPM. A display campaign spent $450 and delivered 150,000 impressions. CPM = (450 ÷ 150,000) × 1,000 = $3.00.
➔ Example 2: Plan your budget. You want 500,000 impressions and expect a CPM of $4. Budget = (4 × 500,000) ÷ 1,000 = $2,000.
➔ Example 3: Estimate your reach. You have a $1,200 budget and a CPM of $6. Impressions = (1,200 ÷ 6) × 1,000 = 200,000.
➔ Example 4: Effective CPM for a CPC campaign. A Search campaign spent $900 on clicks and received 60,000 impressions. Effective CPM = (900 ÷ 60,000) × 1,000 = $15. This lets you compare the cost of visibility in Search with your display or video campaigns.

CPM is one of several pricing models. The right choice depends on what you want a campaign to achieve:

Many advertisers combine them: CPM or vCPM to build awareness at the top of the funnel, and CPC or CPA bidding in Search to capture demand.

A standard impression is counted when an ad is served, even if it loads below the fold and nobody scrolls to it. Viewable CPM only counts impressions that had a real chance to be seen. According to Google's Active View definitions:

➔ A display ad is viewable when at least 50% of its area is on screen for at least one second. For large display ads of 242,500 pixels or more, the threshold is 30% of the area for one second.
➔ A video ad is viewable when at least 50% of its area is on screen while the video plays for at least two seconds.

In Google Ads reports, check Viewable impressions, Viewable rate and Avg. viewable CPM. A low viewable rate on certain placements is a sign that part of your budget is going to inventory people rarely see.

There is no single "good" CPM. Prices vary widely depending on:

➔ Audience and targeting: narrow, high-value audiences cost more to reach than broad ones.
➔ Ad format and placement: video and premium placements usually cost more than standard display.
➔ Industry and competition: more advertisers bidding for the same audience pushes prices up.
➔ Seasonality: CPMs often rise during peak retail periods such as the end-of-year holidays.
➔ Location and device: prices differ between countries, regions and devices.
➔ Ad quality and relevance: relevant, engaging ads tend to win auctions more efficiently.

Instead of chasing an industry average, track your own CPM over time and compare it with the results each campaign delivers.

Your reported CPM assumes every impression was a real chance to reach a person. When part of those impressions come from bots or fraudulent placements, the cost of reaching real people is higher than your report shows.

Simple example: if you pay a $5 CPM and 20% of your impressions are invalid, you are really paying $5 for 800 genuine impressions. Your effective CPM for real people is (5 ÷ 800) × 1,000 = $6.25.

Common causes of wasted impressions include:

➔ Bot traffic that loads pages and ads without a human behind the screen.
➔ Ad stacking and pixel stuffing, where ads are layered or shrunk so nobody can see them.
➔ Low-quality and made-for-advertising sites that exist mainly to sell impressions.

For impression-based fraud, use placement reviews, ads.txt and sellers.json checks, and an ad verification tool. On the click side, ClickSambo checks every click on your Google Ads and Meta Ads campaigns in real time and blocks suspicious sources, so CPC campaigns and the data your bidding relies on stay cleaner. Learn more about how click spam and ad stacking affect your budget.