What is Fill Rate?
Quick Definition: Fill Rate is a vital publisher metric showing the percentage of ad opportunities (requests) that were successfully filled with an ad. It’s the primary measure of inventory efficiency; a low rate signifies wasted ad slots and lost revenue. Optimizing it is key to a healthy monetization strategy.
An Introduction to Fill Rate
Think of your app or website’s ad inventory like a fishing net. Every time you have a space to show an ad, you cast the net; this is an ad request. The Fill Rate tells you what percentage of the time you actually pull up a fish (a paid ad). If you cast your net 100 times but only catch 85 fish, your Fill Rate is 85%, and 15 opportunities were lost. It’s the most direct answer to the question, “When I ask for an ad, how often do I actually get one?”
The core calculation is:
Fill Rate = (Number of Ads Shown (Impressions)/ Number of Ad Requests)×100%
For instance, if your platform made 500,000 ad requests in a day and displayed 475,000 ads, your calculation would be (475,000 / 500,000) × 100, for a Fill Rate of 95%.
The Balancing Act: Fill Rate vs. eCPM
A publisher’s most important strategic challenge is balancing Fill Rate with eCPM (your revenue per 1,000 impressions). These two metrics are often in opposition, controlled by your floor prices (the minimum price you’ll accept for an ad).
- Seeking High eCPM (Price): Setting high floor prices attracts only premium ads, boosting your eCPM. However, fewer advertisers can meet this price, which will decrease your Fill Rate.
- Seeking High Fill Rate (Quantity): Lowering floor prices allows more advertisers to win your inventory, which will increase your Fill Rate but will decrease your average eCPM.
The goal isn’t to maximize one metric, but to find the sweet spot that maximizes total revenue.
Example: A publisher has 2,000,000 ad requests.
- Strategy 1 (Quality Focus): A high floor price results in a $18 eCPM but only a 50% Fill Rate (1,000,000 ads shown).
- Total Revenue: $18,000
- Strategy 2 (Quantity Focus): A low floor price results in a $12 eCPM but a 90% Fill Rate (1,800,000 ads shown).
- Total Revenue: $21,600
In this scenario, prioritizing a higher quantity of filled ads over a higher price per ad led to greater overall earnings.
Key Drivers of Your Fill Rate
Several factors determine your Fill Rate:
- Market Demand: This includes the user’s geographic location (Tier-1 countries like the US have more demand) and the platform choice (iOS vs. Android).
- Publisher Strategy: Your monetization stack is key. Using Ad Mediation to access multiple ad sources dramatically boosts fill rate compared to relying on a single ad network.
- Campaign Rules: Strict floor prices or frequency caps can limit the pool of eligible ads, sometimes intentionally lowering the fill rate in exchange for higher-quality ads or a better user experience.
Why Fill Rate is a Critical Metric
Tracking Fill Rate is essential because it serves as:
- A Core Component of Revenue: Your total earnings depend on both showing ads (Fill Rate) and showing them at a good price (eCPM). You cannot ignore one for the other.
- A Monetization Health Barometer: It’s the most direct indicator of how efficiently you are converting ad opportunities into revenue.
- An Early Warning System: A sudden dip can signal technical problems with an SDK, network outages, or a drop in advertiser demand.
Related Terms
- Ad Mediation: The most common and effective tool used by publishers to increase their fill rate.
- Ad Publisher: An app developer or company that integrates ads into their product, making their user base (inventory) available to advertisers to generate revenue.
- In-App Ads: A monetization model where developers earn revenue by integrating paid advertisements directly into their mobile app’s user experience.
- Rewarded Ads: An opt-in ad that users choose to watch in exchange for a valuable in-app reward.
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