CPI: cost per impression

What is cost per impression (CPI)?

Cost per impression (CPI) is a digital advertising metric that measures the cost an advertiser pays for 1,000 impressions of their ad. An impression occurs each time an ad is displayed to a user, regardless of whether they interact with it. This pricing model allows advertisers to pay based on visibility rather than actions taken. CPI helps marketers understand how efficiently they're purchasing ad visibility across different platforms and campaigns.

How is CPI calculated?

CPI is calculated by dividing the total cost of an advertising campaign by the number of impressions, then multiplying by 1,000. The formula looks like this:

CPI = (Total Campaign Cost ÷ Number of Impressions) × 1,000

For example, if you spend $500 on a campaign that generates 250,000 impressions, your CPI would be: ($500 ÷ 250,000) × 1,000 = $2 CPI

This means you're paying $2 for every 1,000 times your ad appears before your audience.

What's the difference between CPI and CPM?

CPI and CPM (Cost Per Mille) essentially measure the same thing with different terminology. Both metrics calculate the cost per thousand impressions of an advertisement. The term "mille" in CPM comes from the Latin word for thousand. While some marketers might use CPI to refer to the cost of a single impression, in standard industry practice, CPI and CPM are used interchangeably, with CPM being the more commonly used term in most advertising platforms and agencies.

When should you use CPI bidding?

CPI bidding works best when your primary goal is brand awareness or reach. You should consider using CPI bidding when:

You're launching a new product or service and want to maximize visibility quickly. Your campaign focuses on building brand recognition rather than driving immediate conversions. You need to reach a broad audience at the beginning of your marketing funnel. You're running display or video campaigns where impressions matter more than immediate clicks. You want to maintain consistent visibility in highly competitive markets where click costs are prohibitively expensive.

CPI bidding gives you predictable costs for ad exposure, making it easier to budget for awareness-focused campaigns.

How does CPI compare to other advertising metrics?

CPI focuses purely on ad visibility, while other metrics measure different aspects of campaign performance:

CPC (Cost Per Click) measures what you pay when someone clicks your ad. Unlike CPI, which pays for exposure, CPC only charges when users take action. CPC is typically better for direct response campaigns where immediate engagement matters.

CPA (Cost Per Acquisition) measures what you pay for a conversion or completed action (like a purchase or sign-up). This is further down the funnel than CPI, making it ideal for campaigns focused on driving specific business outcomes.

CTR (Click-Through Rate) measures the percentage of people who click after seeing your ad. While CPI helps you understand exposure costs, CTR helps you gauge ad relevance and effectiveness.

The right metric depends on your goals—use CPI when visibility matters most, CPC when engagement is key, and CPA when conversions drive your strategy.