Ad Fill Rates: How low can they go?[+5 Ways to Maximize Fill Rate]

This post was most recently updated on April 18th, 2025

Ad Fill Rate is the percentage of ad requests successfully filled by ads. Calculated as (Ad Impressions / Ad Requests) × 100, it measures how effectively your ad inventory generates revenue. A high fill rate means more ads served, while a low rate indicates missed opportunities.

If you’re experiencing a low ad fill rate on your website, you’re not alone. Many website owners and publishers face this issue at some point. In this article, we will explore the underlying causes of low ad fill rates and provide troubleshooting tips to help you optimize your ad fill rate.

How Ad Fill Rate Works?

Before we dive into the troubleshooting steps, let’s take a moment to understand how ad fill rate works. Ad fill rate is the percentage of ad requests that are successfully filled with advertisements. A high fill rate indicates that most of your ad requests are being fulfilled, while a low fill rate means that a significant number of ad requests are going unfilled.

Now, let’s delve deeper into the intricacies of ad fill rates. Ad fill rates are influenced by various factors, such as the demand for ad inventory, the quality of your website’s content, and the targeting settings you have in place. When an ad request is made from your website, it is sent to an ad network or ad exchange to find a suitable ad to display. The ad network or exchange then evaluates the available ads based on factors like relevance, bid price, and targeting criteria. If a suitable ad is found, it is served to your website, resulting in a successful fill. However, if no suitable ad is available, the ad request goes unfilled, leading to a lower fill rate.

Another factor that can impact fill rate is the ad targeting settings you have set in place. By refining your targeting options, you can increase the likelihood of finding ads that match your audience’s interests and demographics. For example, if your website caters to a specific niche, such as fitness enthusiasts, you can set targeting parameters to attract advertisers who specialize in that area. This targeted approach can result in higher fill rates as advertisers are more likely to bid on ad space that reaches their desired audience.

Why Ad Fill Rate Matters: The Hidden Revenue Lever You Can’t Ignore

A high Ad Fill Rate isn’t just a vanity metric—it’s the lifeblood of your ad revenue. Here’s why optimizing it should be your #1 priority:

1. Revenue Impact: Every Unfilled Ad Request = Lost Money

• Fact: A 10% increase in fill rate can boost ad revenue by 6-15% (PubMatic, 2023).
• Example: If your site generates 100,000 monthly ad requests at a 60% fill rate, you’re missing 40,000 potential impressions. At a $5 CPM, that’s $200/month left on the table—$2,400/year.
• Worst Case: Sites with <50% fill rates lose up to 35% of potential ad earnings.

2. Publisher Performance: Advertisers Favor High-Fill Sites

• Demand Competition: SSPs (Supply-Side Platforms) prioritize publishers with >80% fill rates for premium deals.
• Google’s Algorithm: Sites with consistently high fill rates get better ad inventory and higher-paying campaigns.
• Real-World Impact: A Mediavine study found publishers who improved fill rates from 65% to 85% saw a 22% increase in RPMs.

3. User Experience: The Balancing Act Between Ads & Engagement

• Ad Overload Risk: A 100% fill rate isn’t ideal—it often means low-quality ads, hurting UX.
• Sweet Spot: Top publishers maintain 75-90% fill rates while keeping bounce rates under 40% (Google Analytics benchmarks).
• Mobile Factor: 53% of users abandon sites if ads take >3 seconds to load (Akamai, 2024). Optimizing fill rate reduces latency, keeping visitors engaged.

How low can ad fill rates go?

A low ad fill rate can vary depending on your website’s specific circumstances and the industry you are in. However, as a general guideline, a fill rate below 60% can be considered low and may indicate an issue that needs to be addressed.

Understanding ad fill rates is crucial for website owners and publishers who rely on advertising revenue to sustain their businesses. Ad fill rate refers to the percentage of ad requests that are successfully filled with ads. It is a key metric that measures the effectiveness of your ad inventory management and the overall performance of your advertising strategy.

When your ad fill rate falls below a certain threshold, it can have significant implications for your website’s revenue potential. A low fill rate means that a substantial portion of your ad inventory is going unsold or unutilized, resulting in missed opportunities to generate advertising revenue.

There are several factors that can contribute to a low ad fill rate. One common reason is a lack of demand from advertisers for your specific audience or niche. If your website caters to a niche market with limited advertiser interest, it can be challenging to achieve high fill rates.

Another factor that can impact ad fill rates is the quality and relevance of your content. Advertisers are more likely to bid on ad placements that align with their target audience and brand values. If your content is not attracting advertisers or is not optimized to attract relevant ads, it can negatively affect your fill rate.

Furthermore, your website’s ad placement and layout can also influence the fill rate. Ads that are prominently displayed and integrated seamlessly into the user experience tend to have higher fill rates. On the other hand, ads that are buried in obscure corners or disrupt the user experience may struggle to attract advertisers, resulting in lower fill rates.

Monitoring and optimizing your ad fill rate is essential to maximize your advertising revenue. By analyzing your fill rate data, you can identify trends, patterns, and areas for improvement. Experimenting with different ad formats, placements, and targeting strategies can help increase your fill rate and unlock additional revenue streams.

Ultimately, a low ad fill rate should not be ignored or dismissed. It is a clear indicator that there are opportunities to optimize your advertising strategy and improve your revenue potential. By understanding the factors that contribute to a low fill rate and taking proactive steps to address them, you can enhance the performance of your ad inventory and drive sustainable growth for your website.

Low Ad Fill Rate: Main Causes

Several factors can contribute to a low ad fill rate. Below, we will discuss some common causes:

• Poor ad placement: If your ad units are not strategically placed on your website, they may not receive optimal visibility, leading to lower fill rates. Ad placement plays a crucial role in the success of your ad campaign. It is important to consider factors such as the position, size, and relevance of the ad units. Placing ads in areas where users are more likely to engage with them, such as above the fold or within content, can significantly improve the fill rate. Additionally, ensuring that the ads are seamlessly integrated into the overall design of your website can enhance their visibility and increase the chances of being clicked.

• Ad blockers: The use of ad blockers by your website visitors can significantly impact your ad fill rate. Ad blockers prevent ads from being displayed, resulting in lower fill rates. Ad blockers have become increasingly popular among internet users who want to enhance their browsing experience by avoiding intrusive ads. While ad blockers provide benefits to users, they pose challenges for advertisers and publishers. To mitigate the impact of ad blockers on your ad fill rate, it is important to explore alternative ad formats, such as native ads or sponsored content, which are less likely to be blocked. Additionally, educating your audience about the importance of ads in supporting free content can help to reduce the use of ad blockers.

• Limited ad inventory: If you have a limited inventory of ads available for display, there may not be enough ads to fulfill all your ad requests, resulting in a low fill rate. The availability of a diverse and sufficient ad inventory is crucial for maintaining a high ad fill rate. If your website caters to a niche audience or has a limited number of advertisers, it can be challenging to have a wide range of ads to display. To overcome this, consider expanding your target audience or partnering with more advertisers to increase your ad inventory. Additionally, optimizing your ad targeting and segmentation strategies can help to match the right ads with the right audience, increasing the chances of ad fill.

• Technical issues: Technical issues, such as incorrect ad unit implementation or server configuration problems, can also contribute to a low ad fill rate. Technical issues can have a significant impact on your ad fill rate. It is important to ensure that your ad units are implemented correctly and that the necessary tracking codes are in place. Additionally, regularly monitoring and troubleshooting any server configuration problems can help to prevent interruptions in ad delivery. Collaborating with your ad network or technology partners can provide valuable insights and support in resolving technical issues that may be affecting your ad fill rate.

• High price floors: High price floors can tank your ad fill rate by scaring off advertisers with unrealistic CPM demands. While you might hope for premium bids, most programmatic demand sits at $1.50–$3.50 CPM—set floors too high and you’ll lose 60%+ of potential revenue. The solution? Implement dynamic floor pricing: start low ($0.50–$1.00), then gradually increase while monitoring fill rates, and always segment floors by device and geography (mobile and low-CPM regions need lower thresholds). Tools like Google Ad Manager’s auto-optimization can adjust floors in real-time for maximum revenue. Case studies show publishers boosting fill rates from 58% to 82%—and increasing overall earnings—just by optimizing their price floors.

Is the Low Ad Fill Rate Across All Ad Units?

One of the first steps in troubleshooting a low ad fill rate is determining whether the issue is across all ad units on your website or limited to specific ones. By identifying the specific ad units with low fill rates, you can focus your efforts on optimizing those units.

Regarding ad fill rates, it is important to understand that not all ad units perform equally. Some ad units might have a higher fill rate, meaning they are more likely to display ads, while others might have a lower fill rate, resulting in fewer ads being shown. This discrepancy can be caused by various factors, such as the size and placement of the ad units, the targeting options selected, or the type of ads being served.

By analyzing your website’s ad performance data, you can gain insights into which specific ad units are experiencing low fill rates. This data can be obtained from your ad network or ad server, which typically provides detailed reports on ad impressions, clicks, and fill rates for each ad unit.

Once you have identified the ad units with low fill rates, you must delve deeper into the reasons behind this issue. One possible cause could be insufficient advertisers bidding on the ad space within those units. This could be due to factors such as low demand for specific targeting options or limited competition in the industry niche of your website.

Furthermore, the size of the ad unit can also impact its fill rate. Larger ad units have higher fill rates as they offer more prominent and visually appealing advertising space. Advertisers are often willing to pay more for such ad placements, increasing the likelihood of higher fill rates.

It is worth mentioning that the type of ads being served can also affect the fill rate. Some ad formats, such as display ads or native ads, might have higher demand and fill rates than less popular formats like video or interactive ads. Understanding the preferences of advertisers and your website visitors can help you optimize the ad units accordingly and improve fill rates.

Why are my ad fill rates so low? How do I know the root cause of such bad fill rates?

Here’s an overview of how you can investigate the root cause of a low ad fill rate for publishers, focusing on the aspects you mentioned: viewability, ad format, header bidding setup, invalid traffic, Google policy violations, price floors, ad refresh settings, and SEO.

1. Viewability: Check if your ads are being properly rendered and displayed to users. Low viewability can result from issues such as ad placements, ad blockers, or technical problems on your website.
2. Ad Format: Evaluate the types of ad formats you’re using. Certain formats may have higher demand and better performance than others. Experiment with different formats, such as display ads, native ads, or video ads, to see if they affect your fill rate.
3. Header Bidding Setup: Review your header bidding implementation. Ensure that all demand partners are properly integrated and functioning. Monitor each partner’s performance and optimize your setup to maximize the fill rate.
4. Invalid Traffic: Analyze your traffic sources for any invalid or fraudulent activities. Invalid traffic, including bot traffic or click fraud, can significantly impact your ad fill rate. Use reliable bot blocking tools to detect and filter out suspicious traffic.
5. Google Policy Violations: Make sure your website and ad placements comply with Google’s policies. Violations can result in limited ad serving or lower fill rates. Check for issues like inappropriate content, deceptive practices, or prohibited ad placements.
6. Price Floors: Examine your price floors, which determine the minimum price you’re willing to accept for ad impressions. Setting price floors too high can reduce demand and lower your fill rate. Experiment with different floor levels to find the optimal balance.
7. Ad Refresh Settings: Evaluate your ad refresh settings, if applicable. Automatic ad refreshing can increase impressions but may also decrease fill rate. Find the right balance between refreshing ads and maintaining a good user experience.
8. SEO: Ensure that your website is optimized for search engines. Improving your organic traffic can indirectly impact your ad fill rate by increasing the number of users visiting your site. Focus on relevant keywords, quality content, and effective on-page optimization.

How to Check Ads.txt to verify the correct installation of ad units?

A missing or broken ads.txt file can significantly impact your fill rates. To ensure proper installation of ad units, follow these steps:

1. Check the presence of your ads.txt file: Make sure you have an ads.txt file in your website’s root directory. This file is essential for authorizing ad sellers.
2. Verify ads.txt reporting in GAM: Access your Google Ad Manager (GAM) account and check the ads.txt reporting. Ensure that the file is being crawled and authorized correctly.
3. Reinstall the ads.txt file if necessary: If your ads.txt file is not installed correctly or is missing, reinstall it in the root directory of your website. Then, confirm in GAM that the file is installed properly.
4. Troubleshooting: If the ads.txt file was installed correctly but you’re still experiencing issues, proceed to further troubleshooting steps to identify any potential errors or conflicts.

By following these simplified steps, you can easily verify the correct installation of ad units using the ads.txt file and take the necessary actions to improve your fill rates.

How can I ensure that the ads are displaying correctly?

Manually checking your website to ensure the ads display correctly is crucial for identifying any display issues. Visit your website from different devices and browsers to confirm that the ads are showing up properly. You may need to troubleshoot further if you notice any inconsistencies or errors.

Tips for Improving Your Ad Fill Rate

Improving your fill rate requires a strategic approach. One way to increase fill rate is by optimizing your ad placements. Placing ads in prominent and visible positions on your website can attract more advertisers and increase the chances of finding suitable ads to fill your ad requests. Additionally, ensuring that your website’s content is high-quality and relevant to your target audience can also improve your fill rate. Advertisers are likelier to bid on ad space that aligns with their target audience, increasing the chances of successful ad fills.

Now that we have explored some common causes of low ad fill rates let’s discuss some tips to help you improve your ad fill rate:

1. Strategic ad placement: Experiment with different ad placements on your website to maximize visibility and engagement.
2. Optimize for mobile: With the increasing number of users accessing websites through mobile devices, ensure that your ads are mobile-friendly and are optimized for mobile viewing.
3. Diversify your ad networks: Working with multiple ad networks can increase your chances of filling ad requests, especially if you have limited ad inventory.
4. 🌎 Geo-Targeting: Target visitors or users from countries with the highest ad demand.
5. Consider native ads: Native ads seamlessly blend with your website’s content, providing a better user experience and potentially increasing fill rates.

Monitoring and analyzing your fill rate is crucial for optimizing your ad revenue. By regularly reviewing your fill rate data, you can identify trends and patterns affecting your ad performance. For instance, a sudden drop in fill rate could indicate a technical issue or a change in advertiser demand. Promptly addressing these issues ensures your fill rate remains high and maximizes your ad revenue potential.

Ad Fill Rate Optimization Techniques

1-Optimizing with multiple ad networks

Keep looking for ad networks that can work better for your site. Communicating with different ad networks will let you know the rates they can offer on displaying their campaigns on your site. Thus, this will allow you to maximize not only the fill rate but also the potential earnings of your site.

2-Geo-Targeting

Target visitors or users from countries that have the strongest demand. Look for ad networks that require and work best in countries where most of your site traffic is coming from.

3-Flexi Ad Sizes

Use Flexi ad sizes on your ad placements to achieve higher fill rates for single slot sizes. It works well when the exact slot size isn’t in demand. The largest playable ad size will be the one to display the campaign on a particular ad placement. This will increase the competition, and it will be beneficial for you and the advertiser.

4-Breaking through Ad blocking

Most users prefer to use ad blockers to avoid annoying ads. Even if you are abiding by ad placement policies when serving ads on your website, you can still get affected by ad-blocking apps. Thankfully there are solutions developed to help advertisers break through ad blockers. In addition to the tips mentioned above, there are several optimization techniques you can implement to improve your ad fill rate:

• Monitor and analyze your data regularly to identify trends and patterns that can help you optimize your ad fill rate.
• Experiment with different ad formats and sizes to determine which ones perform the best in terms of fill rate.
• Test different ad networks to find the ones that offer higher fill rates for your website’s audience.
• Continuously optimize your website’s performance to ensure faster loading times, reducing the likelihood of ad requests timing out and resulting in lower fill rates.

Ad Server Setup Checkups

Finally, it’s essential to regularly review and assess your ad serving setup to identify any misconfigurations or technical issues contributing to a low ad fill rate. Work closely with your ad network partners and consider seeking professional assistance.

By implementing these troubleshooting steps and optimization techniques, you can work towards improving your ad fill rate and maximizing your website’s revenue potential.

Remember, addressing a low ad fill rate requires ongoing monitoring, experimentation, and adaptation. Stay proactive and continue to optimize your ad-serving strategy to achieve better results.

Is 100% Ad Fill Rate Possible?

While 100% is rare, aiming for 80-90% is realistic. Excessively high rates may indicate low-quality ads, harming user experience. Platforms like Google AdSense use “Ad Balance” to prioritize both fill rate and ad quality.

Getting the help you need

If you’ve been struggling to maximize the fill rate on your sites, implement the tips we’ve mentioned in this post. However, this process can be time-consuming and get quite complicated so why not let our dedicated team of ad optimizers do it for you? Sign up for a Starter account at MonetizeMore today!

Stop worrying about this issue and let MonetizeMore bust down your low ad fill rates. Get Started here!

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Additional FAQ

What is the fill rate?

The fill rate refers to the number of ads shown compared to the number of ad requests made on a web page. Higher fill rates generally result in better ad revenue for publishers. We talk about increasing fill rates in the post.

How do you increase the fill rate?

There are many different ways of increasing the fill rate of your ads, such as running multiple ad networks, using flexible ad sizes, geo-targeting, and much more. We go into more detail in our blog post.

What is an ad request?

An ad request is where an ad server sends a request to fill an ad unit with an advertisement that happens when the user starts loading the webpage. This process will occur for every ad unit on a webpage. Ad requests can be counted even if no ads were returned from your advertisers.

How do you calculate the fill rate?

Fill rate = ad impressions/ad requests x 100