Advertising Metrics
CPC vs CPM: Cost Per Click vs Cost Per Mille
Two ways to buy and measure paid media. One prices traffic; the other prices reach. CTR is the bridge between them.
Quick Answer
CPC (Cost Per Click) is ad spend divided by clicks. It answers: how much do I pay for each visit?
CPM (Cost Per Mille) is the cost of 1,000 impressions: (Ad Spend ÷ Impressions) × 1,000. It answers: how much do I pay for reach?
CTR (Click-Through Rate) connects them. When CTR is a percent: CPC ≈ CPM ÷ (CTR × 10) and CPM ≈ CPC × CTR × 10.
Side-by-side comparison
| Dimension | CPC | CPM |
|---|---|---|
| Definition | Cost per click | Cost per 1,000 impressions |
| Formula | Ad Spend ÷ Clicks | (Ad Spend ÷ Impressions) × 1,000 |
| Primary goal | Traffic / site visits | Reach / awareness |
| Unit of value | Click | Impression (×1,000) |
| Best paired with | CTR, conversion rate, CPA | CTR, viewability, frequency |
| Risk if optimized alone | Cheap low-intent clicks | Cheap ignored impressions |
Formulas
CPC = Total Ad Spend ÷ Clicks
CPM = (Total Ad Spend ÷ Impressions) × 1,000
CTR = (Clicks ÷ Impressions) × 100
CPC ≈ CPM ÷ (CTR × 10) · CPM ≈ CPC × CTR × 10
Worked conversion example
Spend $5,000, deliver 500,000 impressions, get 10,000 clicks:
- CPM = ($5,000 ÷ 500,000) × 1,000 = $10
- CTR = (10,000 ÷ 500,000) × 100 = 2.0%
- CPC = $5,000 ÷ 10,000 = $0.50
- Check: CPC ≈ 10 ÷ (2 × 10) = $0.50
If creative improves CTR from 1% to 2% at the same $10 CPM, approximate CPC falls from $1.00 to $0.50—without raising bids.
When to use each
Prefer CPM when:
- The goal is brand awareness, reach, or frequency
- You are buying display, video, or social inventory priced on impressions
- You need to forecast how many impressions a budget can buy
Prefer CPC when:
- The goal is website traffic or click-driven funnels
- You are comparing search and social traffic efficiency
- You want a cost that sits closer to CPA (CPA ≈ CPC ÷ conversion rate)
Common mistakes
Optimizing CPC alone. Cheap clicks that never convert inflate CPA. Always check conversion rate and CPA.
Celebrating a low CPM with a dead CTR. Unseen or ignored impressions are not efficient reach.
Comparing search CTR to display CTR. Baselines differ by format—segment reports.
Forgetting currency and attribution windows. Align spend and click definitions with platform billing.
How they connect to CPA and ROAS
- CPA ≈ CPC ÷ conversion rate (or Ad Spend ÷ Conversions)
- ROAS = Revenue ÷ Ad Spend
A “good” CPC or CPM only matters if contribution margin and ROAS hold. Use the CPA Calculator and ROAS Calculator for outcome metrics.
Which should you track?
Both—plus CTR. Track CPM for reach cost, CPC for traffic cost, and CTR as the quality bridge. For the full walkthrough, see the CPC, CPM & CTR guide.
Sources
Formulas match the live Metricalytics calculators. Channel benchmarks elsewhere on the site are directional; prefer your account history. See our disclaimer.
Frequently Asked Questions
What is the difference between CPC and CPM?
CPC (Cost Per Click) is what you pay per click: Ad Spend ÷ Clicks. CPM (Cost Per Mille) is what you pay per 1,000 impressions: (Ad Spend ÷ Impressions) × 1,000. CPC optimizes for traffic; CPM optimizes for reach.
How do you convert CPC to CPM?
When CTR is a percent, approximate CPM ≈ CPC × CTR × 10. Example: $1.00 CPC at 2% CTR ≈ $20 CPM. You need CTR (or both clicks and impressions) to convert accurately.
How do you convert CPM to CPC?
When CTR is a percent, approximate CPC ≈ CPM ÷ (CTR × 10). Example: $20 CPM at 2% CTR ≈ $1.00 CPC. Higher CTR lowers effective CPC for the same CPM.
When should I use CPC vs CPM bidding?
Use CPM (or reach/impression goals) when brand awareness matters and you care about cost of exposure. Use CPC (or traffic/conversion goals) when you need site visits or downstream conversions. Always connect both to CPA and ROAS.
Is a low CPM always better than a low CPC?
No. A cheap CPM with near-zero CTR wastes budget on ignored impressions. A higher CPM with strong CTR can produce a lower effective CPC and better CPA. Judge efficiency by outcomes, not the buying model alone.