CPM Formula

The CPM Formula

The CPM formula calculates the cost of 1,000 ad impressions. It is the standard metric for buying and reporting on impression-based advertising campaigns.

The formula is:

This formula applies universally across all ad platforms — Google Ads, Meta, LinkedIn, TikTok, programmatic networks, and Chinese platforms such as Douyin, Kuaishou, and Little Red Book (Xiaohongshu).

What Each Variable Means

Cost

The total amount spent on the campaign. This is the numerator in the formula — the value you are dividing. Cost is typically expressed in the reporting currency of your ad platform (USD, EUR, CNY, etc.).

Impressions

The total number of times an ad was served and counted. One impression equals one ad served, regardless of whether the user actually saw or clicked on it. Impressions are the denominator — the value you are dividing by.

1,000

The fixed multiplier that converts the result from cost per single impression to cost per thousand impressions. Without multiplying by 1,000, the result would be a fractional dollar amount per impression — impractical for reporting and comparison.

Why the Formula Multiplies by 1,000

The number 1,000 is built into the definition of CPM. CPM literally means Cost Per Mille — and mille is Latin for one thousand.

Multiplying by 1,000 converts a raw cost-per-impression rate into a readable dollar figure. For example:

A campaign costs $100 and delivers 100,000 impressions.

While mathematically correct, $0.001 per impression is difficult to work with in reporting. Scaling by 1,000 gives:

Now the result is a clean dollar amount per 1,000 impressions — easy to compare, report, and benchmark.

CPM Formula Example

Reverse CPM Formulas

The CPM formula can be rearranged to solve for any variable when the other two are known. This is useful for campaign planning and budget forecasting.

Calculate Total Cost from CPM and Impressions

You want 500,000 impressions at a $6 CPM. Estimated cost: (500,000 ÷ 1,000) × $6 = $3,000.

Calculate Impressions from CPM and Budget

You have a $4,000 budget and a $8 CPM. Expected impressions: ($4,000 ÷ $8) × 1,000 = 500,000.

Calculate CPM from Cost and Impressions

You spent $2,500 and received 400,000 impressions. CPM = ($2,500 ÷ 400,000) × 1,000 = $6.25.

CPM Formula in Excel and Google Sheets

You can use the CPM formula directly in spreadsheets. Here are the standard formulas:

Calculate CPM

If Cost is in column A and Impressions is in column B:

Calculate Cost from CPM and Impressions

If Impressions is in column A and CPM is in column B:

Calculate Impressions from Cost and CPM

If Cost is in column A and CPM is in column B:

Pro tip: Format CPM cells as currency to display the dollar sign automatically. Use absolute references (e.g., $A$1) if you are copying formulas across multiple rows with a fixed CPM rate.

CPM vs eCPM vs RPM vs CPI

These four metrics all use cost-per-thousand or revenue-per-thousand logic, but they serve different roles in the advertising ecosystem.

Common CPM Formula Mistakes

Even experienced marketers sometimes make these errors when applying the CPM formula:

Using clicks instead of impressions.

CPM is specifically an impression-based metric. If you divide spend by clicks, you get CPC (Cost Per Click), not CPM.

Confusing impressions with reach or unique viewers.

Impressions count every ad served. Reach counts unique users. If the same user sees your ad five times, that is five impressions but one reach. Always use impressions when calculating CPM.

Forgetting to multiply by 1,000.

This is the most common CPM formula error. Without multiplying by 1,000, you get cost per single impression — which is not CPM and will not match platform-reported figures.

Comparing CPM across incompatible channels.

A $5 CPM on LinkedIn and a $5 CPM on TikTok represent completely different value. Always compare CPM within the same platform, format, and targeting scope.

Mixing currencies without converting.

If your ad spend is in USD but impressions are from a CNY-platform report, convert to a single currency first before calculating CPM.

Frequently Asked Questions

What is the exact CPM formula?

CPM = (Cost ÷ Impressions) × 1,000. Cost is the total campaign spend in dollars, impressions is the total number of ad servings, and the result is expressed as dollars per 1,000 impressions.

Why do you multiply by 1,000 in the CPM formula?

Because CPM is defined as Cost Per Mille — cost per one thousand impressions. The 1,000 is part of the definition, not an arbitrary multiplier. Without it, you would get cost per single impression, which is not CPM.

How do I calculate cost from CPM?

Rearrange the formula: Cost = (Impressions ÷ 1,000) × CPM. For example, 400,000 impressions at a $6 CPM costs $2,400.

How do I calculate impressions from CPM?

Rearrange the formula: Impressions = (Cost ÷ CPM) × 1,000. For example, a $5,000 budget at a $4 CPM delivers 1,250,000 impressions.

What is the difference between CPM and eCPM?

CPM is an advertiser metric (cost per thousand impressions bought). eCPM is a publisher metric (effective revenue per thousand impressions earned). Both use the same × 1,000 structure, but CPM uses cost in the numerator while eCPM uses revenue. If you need a beginner-friendly walkthrough, read our step-by-step CPM calculation guide.

Conclusion

The CPM formula — Cost ÷ Impressions × 1,000 — is the foundation of impression-based advertising. Understanding each variable and how to rearrange the formula helps you plan budgets, forecast results, and evaluate campaign efficiency with confidence.

For advertisers just getting started, read our step-by-step CPM calculation guide for a beginner-friendly walkthrough.