eCPM (effective Cost Per Mille) is often misunderstood. This guide breaks down what eCPM really means, how to calculate it correctly, and which metrics actually drive revenue.

What Is eCPM? A Clear Guide to Effective Cost Per Mille

eCPM represents the effective cost per thousand impressions. It normalizes revenue across different pricing models (CPM, CPC, CPA) into a single comparable metric.

The basic formula:

eCPM = (Total Revenue / Total Impressions) × 1000

What Is eCPM? A Clear Guide to Effective Cost Per Mille

eCPM allows you to:

Compare performance across different demand sources
Evaluate pricing strategies
Optimize your revenue mix
Make informed decisions about floor prices

The eCPM Misconception

Many publishers focus solely on maximizing eCPM. This is a mistake. Here's why:

Scenario A: 1000 impressions at $10 eCPM = $10 revenue

Scenario B: 10,000 impressions at $5 eCPM = $50 revenue

Scenario B generates 5x more revenue despite half the eCPM. This is why you need to balance eCPM with volume.

Metrics That Actually Matter

1. Revenue Per Session (RPS)

This is the ultimate metric:

RPS = Total Revenue / Total Sessions

RPS accounts for both pricing (eCPM) and volume (ad load), giving you the complete picture of monetization efficiency.

2. Fill Rate

High eCPM means nothing if you can't fill inventory:

Fill Rate = (Filled Requests / Total Requests) × 100

Optimize for the revenue sweet spot, not maximum eCPM.

3. Revenue Mix

Break down revenue by source:

Direct campaigns
Programmatic guaranteed
Private marketplace (PMP)
Open exchange

A healthy mix ensures stability and reduces dependence on any single source.

4. Session eCPM

Rather than per-impression eCPM, calculate per-session:

Session eCPM = (Session Revenue / 1) × 1000

This accounts for variation in impressions per session.

Optimizing Your eCPM Strategy

Segment Your Analysis

Calculate eCPM by:

Geography: Premium markets command higher eCPMs
Device type: CTV typically outperforms mobile
Time of day: Prime time drives higher pricing
Content category: Some genres attract premium advertisers
Ad position: Pre-roll often commands premium pricing

Dynamic Floor Optimization

Test different floor prices by segment. Sometimes lowering floors increases fill enough to boost overall revenue despite lower eCPM.

Demand Density Analysis

Track bid density—how many bids do you receive per request? Low density suggests your inventory isn't reaching enough buyers.

The eCPM-Fill Rate Curve

There's typically an inverse relationship between eCPM and fill rate. As you increase floors (boosting eCPM), fill rate drops.

The optimal point is where eCPM × Fill Rate is maximized. This varies by inventory segment.

Benchmarking eCPM

Industry Averages (2025)

CTV Pre-Roll: $15-$35 eCPM
CTV Mid-Roll: $12-$28 eCPM
Mobile Video: $8-$18 eCPM
Desktop Video: $10-$22 eCPM

Note: Actual rates vary significantly based on content quality, audience, and targeting capabilities.

Seasonal Variation

eCPMs fluctuate throughout the year:

Q4: Highest eCPMs (holiday shopping)
Q1: Lowest eCPMs (post-holiday slowdown)
Q2-Q3: Moderate, with spikes around events

Advanced eCPM Metrics

Net eCPM

Account for costs:

Net eCPM = Gross eCPM - (Ad Serving Costs + Revenue Share)

This shows your actual take-home revenue per thousand impressions.

Lifetime Value (LTV) eCPM

For subscription businesses, consider long-term value:

LTV eCPM = (Ad Revenue + Subscription Value) / Impressions × 1000

Engagement-Adjusted eCPM

Weight eCPM by completion rate:

Adjusted eCPM = eCPM × Completion Rate

This rewards ads that viewers actually watch.

Common Pitfalls

Averaging Averages

Never average eCPMs directly. Always go back to revenue and impressions:

Wrong: (eCPM1 + eCPM2) / 2

Right: (Revenue1 + Revenue2) / (Impressions1 + Impressions2) × 1000

Ignoring Discrepancies

If your reported eCPM and advertiser eCPM differ significantly, you have a measurement problem that needs fixing.

Optimizing in Isolation

eCPM optimization affects user experience, which impacts retention and lifetime value. Always consider the bigger picture.

Building a Dashboarding Strategy

Daily Monitoring

Track these metrics daily:

Overall eCPM trend
Fill rate by source
Revenue per session
Top segments by revenue

Weekly Deep Dives

Analyze weekly:

Segment-level performance
Demand source mix
Anomalies and outliers
Competitive positioning

Set Up Alerts

Configure alerts for:

eCPM drops >15% day-over-day
Fill rate drops >10%
Revenue per session declines
Unusual discrepancy rates

Conclusion

eCPM is a useful metric, but it's not the be-all-end-all. Focus on holistic revenue optimization—balancing eCPM, fill rate, ad load, and user experience.

The publishers who succeed aren't those with the highest eCPM, but those who maximize revenue per session while maintaining a great viewer experience.