Fill Rate
The percentage of ad requests that are successfully filled with a paid advertisement.
What is Fill Rate?
Fill rate measures the percentage of ad requests from your site that result in a paid advertisement being served. When a user loads a page on your site, each ad slot sends a request to your ad network or ad server. If a paying advertiser's ad is returned, that request is "filled." If no ad is available, the request goes unfilled, and the slot either shows a blank space, a house ad, or triggers a passback to another network.
A 100% fill rate means every single ad request received a paid ad. In practice, most publishers see fill rates between 70-95%, depending on their traffic quality, geography, and ad setup.
How It's Calculated
Fill Rate = (Filled Impressions / Total Ad Requests) x 100
If your site sent 100,000 ad requests and 85,000 were filled:
Fill Rate = (85,000 / 100,000) x 100 = 85%
Why It Matters for Publishers
Every unfilled impression is lost revenue. If your fill rate is 80%, you are leaving 20% of your potential ad inventory unused. However, chasing a 100% fill rate at any cost can be counterproductive — accepting very low-paying ads to fill every slot can drag down your overall eCPM and degrade user experience.
The key is finding the balance between fill rate and eCPM. A 90% fill rate at $3 eCPM generates more total revenue than a 100% fill rate at $2.50 eCPM if you have enough traffic volume.
Tips for Optimization
- Use multiple demand sources: Header bidding or waterfall setups with 5-10 demand partners dramatically improve fill rates by creating competition for every impression.
- Configure passbacks: When your primary network can't fill, pass the request to a backup network rather than showing a blank space.
- Adjust floor prices carefully: High floor prices improve eCPM but can tank fill rate. Test different floor levels to find the optimal balance for your traffic.
- Audit unfilled impressions by geo: Traffic from regions with low advertiser demand naturally has lower fill rates. Consider different strategies for different geographies.
- Use ad refresh carefully: Refreshing ads can create additional fill opportunities, but only when users are actively engaged with the page.