CPM, CPC & CTR Glossary — Digital Advertising Metrics Explained
Bikash Roy
Online Research Specialist · SEO Strategist · Web Developer
Bikash personally verifies every calculator against official standards (WHO, NIH, government data). Online research specialist, SEO strategist, and web developer with 10+ years building accurate digital tools.
Full bio →Digital advertising comes with its own shorthand — CPM, CPC, CTR, CPA — and mixing them up is one of the easiest ways to misread a campaign report or blow a budget. This glossary defines each metric precisely, shows the formula behind it, and explains how they relate to one another so you can convert between them with confidence.
The Core Metrics
| Term | What it means | Formula | Unit |
|---|---|---|---|
| Impression | One instance of an ad being served or loaded on a page or app | Counted directly, not calculated | count |
| CPM (Cost Per Mille) | Cost for every 1,000 impressions — the standard pricing unit for display, video, and social inventory | (Cost ÷ Impressions) × 1000 | $ per 1,000 impressions |
| CPC (Cost Per Click) | Total cost divided by the number of clicks an ad received | Cost ÷ Clicks | $ per click |
| CTR (Click-Through Rate) | Share of impressions that resulted in a click | (Clicks ÷ Impressions) × 100 | percent |
| CPA (Cost Per Acquisition) | Cost divided by the number of conversions — sales, leads, or sign-ups | Cost ÷ Conversions | $ per conversion |
| eCPM (Effective CPM) | Normalizes any pricing model — CPC, CPA, or flat fee — back onto a CPM basis for apples-to-apples comparison | (Total Cost ÷ Impressions) × 1000 | $ per 1,000 impressions |
“Mille” is Latin for thousand — that’s where the “M” in CPM comes from, not “million.” The convention was carried over from print advertising and standardized for digital media by the Interactive Advertising Bureau (IAB), the industry body that maintains the official glossary of interactive ad terms.
How CPM, CPC, and CTR Connect
These three metrics aren’t independent. CTR is the bridge between an impression-based price (CPM) and a click-based price (CPC). If you know two of the three, you can derive the effective value of the missing one:
Effective CPC = CPM ÷ (CTR × 10)
Effective CTR = CPM ÷ (CPC × 10)Example: a campaign runs at an $8 CPM with a 2% CTR. Effective CPC = 8 ÷ (2 × 10) = $0.40. In other words, a display campaign priced by impressions is, in effective terms, costing $0.40 per click — which lets you compare it directly against a CPC-priced search campaign on equal footing.
Use the CPM calculator to compute CPM, cost, or impressions directly, then add your click count to see CPC and CTR calculated automatically from the same campaign numbers.
Impressions vs. Viewable Impressions
Not all impressions are equal. The IAB and Media Rating Council (MRC) define a viewable impression as one where at least 50% of the ad’s pixels were in the browser’s visible, in-focus area for a continuous 1 second (2 seconds for video). An impression can be technically “served” without ever being viewable — for example, an ad that loads below the fold that the user never scrolls to.
This distinction matters when you read a CPM figure: a raw served-impression CPM will always look cheaper than a viewable-impression CPM (vCPM), because the denominator used to calculate it is larger. Google Ads and most demand-side platforms let you bid and report on either basis — see Google’s guide to bidding on viewable impressions for how vCPM bidding works in practice. For more on how this trips people up, see common CPM calculation mistakes.
Typical CTR Ranges by Ad Type
| Ad type | Typical CTR range |
|---|---|
| Display / banner ads | 0.3%–1%, average ~0.46% |
| Search ads | 2%–6% |
| Social feed ads | 0.5%–1.5% |
| Video pre-roll / in-stream | 0.2%–0.6% |
These ranges vary by industry, creative quality, and targeting precision — treat them as a rough sanity check, not a hard target. See CPM benchmarks by platform in 2026 for the cost side of this same comparison, and how to use CPM to budget your ad campaign for turning these numbers into an actual spending plan.
Quick Formula Reference
CPM = (Cost ÷ Impressions) × 1000
CPC = Cost ÷ Clicks
CTR = (Clicks ÷ Impressions) × 100
CPA = Cost ÷ Conversions
eCPC = CPM ÷ (CTR × 10)Keep these five formulas on hand and you can convert between any impression-based, click-based, or conversion-based pricing model a platform reports back to you.