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What Is Ad Fill Rate and How You Should Optimize It

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If you have a website or an online business, the chances are you’ve dabbled in online advertising. Most of the two billion websites on the internet rely on ad revenue to monetize their sites. With such huge numbers at play, it’s evident that the competition is fierce. That is why publishers worldwide have been looking for ways to maximize ad impressions for years now, and understanding all the intricacies of ad fill rates has proven to be crucial to achieving that.

Regardless of your level of experience in the digital advertising industry, you’re likely facing the same issue as many other publishers — achieving high fill rates at optimal eCPM. That is why we decided to write an article to help you better grasp ad fill rates and optimize them for maximum revenue. But first, let’s start with the basics.

What Is Ad Fill Rate

Ad fill rate represents the ratio between the number of successfully delivered ads versus the number of ad requests made by the ad server. In other words, it showcases the success rate of all ad calls made by your ad server.

If you want to find out your site’s ad fill rate, you can easily calculate it using the following formula:

an infographic illustrating how to calculate ad fill rate
How to Calculate Ad Fill Rate

Let’s say your website has 10,000 monthly visitors. For most publishers, that will result in 10,000 ad calls, but the reality is not all of them will result in an ad displaying. So if an ad shows up successfully for 6,500 of these 10,000 visitors, that means your website has a 65% fill rate.

Do note that many factors can influence ad fill rates and that they are ever-changing. You may achieve high fill rates one month, while the other you may experience a significant drop due to many internal and external factors (more on those later). 

Considering that ad fill rate illustrates how many ad calls managed to return an ad, it should be evident why publishers wish to maximize it. So aiming for that 100% fill rate should be a no-brainer, right?

Well, not necessarily. And here’s why…

Can (and Should) You Achieve 100% Fill Rate?

Unless you’re new to the online advertising industry, you should know that achieving a 100% ad fill rate is next to impossible.

But what if it were possible? After all, some ad networks let you set your fill rates manually. Doesn’t more ads mean more revenue?

Not always. Your profit depends on more than ad quantity since different ads have varying CPM. Having high fill rates won’t make you more revenue if you sacrifice CPM to achieve them. That is why it’s sometimes better to set your target fill rates lower to guarantee you get better-paying ads. 

One of the best ways to balance fill rate and CPM is to aim for the highest possible fill rates before your CPM starts plummeting. For instance, if your average CPM is 2.20 at 65% fill rates and drops to 1.15 at 80% fill rates, you’re better off sticking to the former.

Aside from the above, there are two more reasons aiming for lower fill rates but higher CPM might be better for some publishers:

  • Server Fess — Publishers who pay server fees per impression will benefit more from fewer ads with higher CPM than vice-versa.
  • Ad Quality — The higher fill rates you have, the greater the odds of low-quality ads slipping through. Low-quality ads can cause various issues like slowing down your website, having trouble loading, and hurting your site’s user experience.

At the end of the day, whether you choose to chase higher or lower fill rates will be entirely up to you. No website is the same, and what fits one publisher may not be the best choice for another. So adjust your goals based on your site’s content and business needs.

6 Possible Reasons Your Fill Rate Isn’t 100%

6 possible reasons your ad fill rate isn't 100%
Possible Reasons Your Ad Fill Rate Isn’t 100%

Although aiming for a 100% fill rate isn’t always the best choice, sometimes it’s the right one. One of the biggest challenges such publishers will face is keeping their fill rates at 100% consistently. Why? Because there are many factors that could impact your fill rates negatively.

1. Technical Errors

Online advertising technology is incredibly complicated. From communication between ad exchanges and ad fraud detection to ad verification, there’s always so much going on behind the scenes. With so many processes taking place simultaneously, many things can go wrong on the technical side of things.

Dealing with these technical errors can be challenging for publishers without a dedicated ad ops team. So if you’re having trouble with failed ad calls, various VAST errors, or other technical difficulties, you might need to expand your team to ensure higher fill rates.

2. High Competition or Lack of Demand

One of the most common problems publishers face when trying to boost their fill rates is lack of demand. Sometimes, businesses operate in niche industries where they’ll have trouble filling their ad inventory. Whether their ad networks have a low supply or advertisers don’t want to advertise on their websites, you won’t be able to do much about this. If you find yourself in such a predicament, you’d be best off trying to maximize your CPM.

Another frequent scenario is that publishers operate in a highly competitive niche. In such cases, publishers should try their hand at header bidding. Implementing this advanced programmatic technique can help you maximize CPM through real-time bidding. As many as 65% of U.S. publishers are already using header bidding; it proved to be an excellent way to compensate for lower fill rates in competitive industries. So if you’re facing similar challenges, this might be the perfect solution.

3. Latency Issues

Latency is also a frequent reason for underperforming fill rates. Why? Because it can delay ad rendering and make users scroll away or leave the page before an ad loads. If your site has a history of slow ad load times, demand-side platforms may choose to serve ads on other, better-performing sites. 

If your website has latency issues, you might want to consider getting a CDN or changing your hosting provider.

4. Device Compatibility

When looking to increase fill rates, publishers must take into account mobile visitors. Some ads may not be compatible with all browsers, devices, and operating systems. So if you’re using any such ads, you’re losing out on a chunk of your audience.

Regardless of whether you’re into mobile video advertising or are targeting broader audiences, implementing proper mobile ad formats is crucial to maximizing fill rates. Just make sure to choose the formats with high supply, so you don’t enter an overly competitive market.

5. Ad Blockers

Ad blockers have been putting a dent in publishers’ pockets for years now. When it comes to fill rates and ad-blocking software, all is well if they block ad calls. However, some ad blockers inhibit ad networks instead. These give publishers headaches since add-ons don’t stop ad requests, just prevent the ads from appearing. That means your fill rates go down the drain!

So what’s the best way to circumvent ad blockers? That depends on many factors, such as the types of ads you’re serving. For instance, one of the best techniques for video advertisers is probably server-side ad insertion. With this method, publishers can insert their ads into a single video stream, concealing it from ad blockers. 

But if you’re not too keen on video ads, there are a few other ways you can deal with ad-blocking software. You can read more about them here.

6. Reporting Discrepancy 

The last but not less common issue publishers may face is reporting discrepancy. Considering that ad servers and demand partners count impressions differently, publishers should expect to see a disparity in fill rates between the two. Unfortunately, you can’t do anything about this issue but consider it when measuring fill rates.

What’s the Average Fill Rate in the Industry?

If you’re looking at your website’s 40% fill rate and are thinking you’re doing poorly, don’t. Most ad networks offer 20% to 30% fill rates as they prefer to provide higher eCPM at the expense of fill rates. However, Google AdSense is an exception to this rule as it has significantly more ad supply.

The above is why most publishers nowadays use more than one ad network to monetize their sites. Having multiple ad providers will boost your fill rates since you’ll get several opportunities for your ad calls to return an ad. This practice has become an industry staple, making it hard to name an industry-average fill rate since it depends on so many factors like:

  • How many ad networks a website is using,
  • The quality of said ad networks,
  • The competitiveness of your niche,
  • And more…

So always take all of these elements into account when measuring your fill rates against your competitors.

How to Optimize Ad Fill Rate

Even though it’s next to impossible to develop a fill rate benchmark you should aim for, that doesn’t mean you cannot optimize them. If you want to achieve the best possible fill rates for your industry while maintaining good CPM, there are a few things you can do:

  • Perfect Your Targeting — Leveraging advanced targeting options like contextual and behavioral targeting is crucial for serving high-quality ads. Displaying only relevant ads will boost your site’s user experience and can significantly improve your bottom line.
  • Get a Quality Ad Network — Your ad network’s quality and ad supply will significantly impact your fill rates. Selecting a small ad network is a bad idea for larger websites as they won’t meet the volume of your demand, thus providing low fill rates.
  • Improve Your Site’s Speed — Having a quick and responsive website is vital for user experience and ad performance. More responsive websites load ads faster, minimizing the risk of users leaving the site or scrolling down before viewing your ads.
  • Optimize for Multiple Ad Formats — Ensure higher fill rates by including multiple ad sizes to fit the broadest range of devices.

Keep the above tips in mind, and you’ll be one step closer to getting those high fill rates you’re looking for! 

Best of luck to you!

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