CTR, CPC, CPM, ROAS, and Conversion Rate Explained

Marketing metrics are useful only when the numerator, denominator and business meaning are clear. CTR, CPC, CPM, ROAS and conversion rate describe different stages of a campaign; one cannot stand in for the others.

Use the formulas to understand what happened, then add attribution, margin and campaign objective before deciding whether performance was good.

CTR: clicks divided by impressions

Click-through rate (CTR) compares clicks with impressions. Google Ads defines CTR as clicks divided by impressions. Its current explanation is available in the Google Ads CTR documentation.

Formula: CTR = clicks ÷ impressions × 100

If an ad receives 120 clicks from 10,000 impressions, CTR is 1.2%. That tells you something about how often an impression became a click; it does not tell you whether the clicks were profitable.

CPC: spend divided by clicks

Average cost per click (CPC) expresses the average amount paid per click. Google’s average CPC guidance describes it as total click cost divided by total clicks.

Formula: CPC = ad spend ÷ clicks

If you spend $300 for 150 clicks, average CPC is $2. A low CPC can be attractive, but cheap clicks have little value if they do not reach the right audience or complete the desired action.

CPM: cost per thousand impressions

CPM standardizes the cost of buying 1,000 impressions.

Formula: CPM = ad spend ÷ impressions × 1,000

It is commonly useful for impression-based media planning and awareness comparisons, but it says nothing by itself about clicks or conversions.

Conversion rate depends on your denominator

A conversion rate compares defined outcomes with the eligible opportunities you choose to measure.

Example: if 50 purchases come from 2,000 sessions, the session-to-purchase conversion rate is 2.5%.

Before comparing conversion rates, confirm that “conversion” means the same thing and that both reports use the same denominator. A lead-form completion rate based on clicks is not directly comparable with a purchase rate based on sessions.

ROAS: attributed revenue value divided by ad spend

Google defines return on ad spend using conversion value relative to advertising spend. See its ROAS glossary entry.

Formula: ROAS = attributed revenue or conversion value ÷ ad spend

If $1,000 of ad spend is credited with $4,000 in revenue, ROAS is 4.0, often expressed as 400% or 4:1.

That is not the same as profit. Product cost, staff, agency fees, refunds, tax, logistics and overhead may sit outside the ratio. Google’s ROI guidance makes the broader distinction between revenue and costs.

Why attribution changes the story

ROAS and conversion counts depend on which interactions receive credit. Different platforms and attribution settings can assign value differently. Record the attribution model, date range and conversion definitions before comparing reports.

Match the metric to the campaign goal

• Awareness: impressions, reach and CPM may matter more than immediate ROAS.
• Traffic: CTR and CPC can reveal response and acquisition cost at the click stage.
• Lead generation: cost per lead and qualified-lead rate add context to click metrics.
• E-commerce: conversion rate, revenue, ROAS and contribution margin may all matter.

Use calculators without losing context

EseoGen’s marketing tools library includes calculators such as a ROAS Calculator. A calculator can apply a formula consistently; it cannot decide whether the attributed revenue is accurate or whether the result covers your full business costs.

The safest habit is to keep the formula, definitions, attribution and business objective beside the number. Metrics become useful when they answer a defined question—not when they are treated as universal scores.