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What is Ad Fill Rate and Should You Aim For 100%?

Ad Fill Rate
Optimizing to hit the threshold percent would yield you the best results.

2 billion – That’s the number of websites existing today. And for most of them, running ads is the only source of income.

For publishers, the aim is to monetize each and every page view or impression at the best possible price. This is where the fill rate comes into existence. Understanding ad fill rates will eventually help you understand how the ad network operates and how you can maximize your revenue.

Table of Content

What is the ad fill rate?

The ad fill rate is the ratio between the number of ads delivered to the number of ads requested by the ad server.  Mathematically, ad fill rate is calculated by using the below formula:

Ad Fill rate = (Total Ad Impressions / Total Ad Requests)* 100

Ad Fill Rate Formula

As much as the publisher wants all ad requests to be returned with an ad, advertisers want their ads to serve only the right audience at the right time.

So, it’s not easy to get a 100% fill rate all the time. That being said, you can consistently maintain your fill rate at 100 percent provided you followed all the best practices. The fill rate helps a publisher to understand how their inventory is being utilized and validate the market demand.

To understand this better, let’s take a simple example. You put up 100 ad inventories on different pages of your website, your fill rate is the percentage of ads you ‘actually display’ on the inventories. Even if you have 100 ad inventories and managed to display ads only on 85 ad inventories, then your fill rate is 85%.

100% fill rate – Is it good or bad?

A good fill rate conveys the inventories are monetized well and have the right demand partners. That being said, it is important to ensure your eCPM isn’t falling to get your fill rates up. Some publishers compromise eCPM to fill their ad placements all the time.

In fact, AdSense, the largest ad network has a feature called ‘Ad Balance’ to set your fill rate. Let’s say you set the fill rate to 100, AdSense algorithm will try its best to fill 100% of your impressions.

Similarly, when you set it to 60, it only fills your inventory up to 60%. But this time, it has the leverage of accepting only the highest paying ads as you just need 60 percent to show up. So, there’s no way you could say 100% fill rate yields the best revenue unless you consider other factors including eCPM, ad quality, and page load time.

Ideally, you should aim to have both a higher fill rate and a higher CPM. The fill-rate percentage point above which your CPM starts to plummet should be the threshold. Thus, optimizing to hit the threshold percent would yield you the best results.

Note: The threshold value isn’t constant and varies based on seasonal factors.

Why your fill rate isn’t 100%?

We just said a 100% fill rate isn’t always good. But in some cases, the higher the fill rate, the higher the revenue. Every time you fail to get an ad for the pageview, you’re losing revenue. If you need to show an ad, regardless of how much it’s going to pay you ($0.5 CPM or $5 CPM), you need to get the 100 percent fill rate consistently.

There are a lot of concerning instances that make your ad request to return empty-handed.

Technical errors

Adtech is complex and the supply chain is longer than you think. From ad fraud detection to ad verification to post-analytics, there are vendors all around the ad serving system to measure the effectiveness of the ad campaigns.

From the moment a user loads your page to the ads getting rendered, you can witness hundreds of events happening in milliseconds. This means you need to be technically strong and have an AdOps team to minimize the errors.

Lack of demand

Site owners are of the view that it is easy for them to sell their ads one way or another. However, this is not possible with most ad networks due to the sole reason that they do not have enough ads to fill your site.

69% of the top 10,000 sites have implemented header bidding as per the Header Bidding Industry Index by Kevel (Src).

Daisy-chaining multiple ad networks leads to increased load time or deprecated CPM. That’s why the publishers are shifting to header bidding solutions.


Some ads may not render on all browsers/devices/OS. The browser might be outdated, the format is not supported by the current version, etc. are some of the reasons.

Make sure you’re running the right mobile ad formats as advertisers want to target users on mobile these days. The best way is to handpick the formats and ad sizes with exceeding demand.


Latency in Digital advertising can delay ad rendering and cause the user to leave the page before the ad appears. If your site continues to have the issue, demand partners would prefer to display ads on other sites, but not on yours. This eventually leads to lower fill rates.

Reporting discrepancy

Ad servers count an ad impression when the ad request is sent to the demand partners whereas the demand partners count the impression only when the ad is rendered to the user. This means you could see the discrepancy in fill rates and this costs you revenue.

Ad Blockers

Some ad blockers block ad networks instead of ad calls. Thus, allowing an ad request but preventing ad appearance. At the end of the day, you would see lower fill rates even though you’ve optimized everything.

What’s the solution?

There are many proven strategies to help you offset the lost revenue.

Average Ad Fill Rate

If the fill rate of a network is high, its eCPM will be lower than normal thus explaining why most ad networks have a fill rate between 20-30%.

The prime means of boosting a website’s fill rate is through the use of a reputable advertising network with a wide selection of publishers. A majority of ad networks offer a fill rate of 25-50% which is not only unambitious but also creates difficulty in monetization. This may be due to the sole reasons that they have few advertisers and too many publishers thus creating excess supply (publisher inventories) but not enough demand (advertisers). Thus providing the publisher a lower fill rate.

If you wonder what your average ad fill rate should be, there is no standard answer you could refer to. We recommend you implement header bidding to capture as many demand partners as possible. This drastically increases your ad fill rate.

Ways to Maximize Your Fill Rate

You can maximize your fill rate by:

  • Header Bidding
  • Geo-targeting
  • Flexible Ad Units
  • Viewable Placements

Learn the detailed implementation here.

What’s Next?

Ad fill rate is one of the most important metrics you need to look at when determining the performance of your ad campaigns. If you’re doing everything right and your click-through rate is good, but your ad fill rate is not up to par, then you are definitely going to lose money in the long run and your overall revenue will be devastated. So, try the strategies listed in this article and let us know it goes.

Already tried but didn’t help? Get in touch with us to get customized solutions for your website.

Automatad Team

At Automatad, we help publishers to monetize better without hampering the user experience. Our products are live across hundreds of publishers, earning them incremental ad revenue with every passing second. You can request a free audit to get an estimated revenue uplift today.

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