What is Ad Fill Rate?

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Online marketing is a complicated affair, one that necessitates both the right tools and approach. Many online advertisers focus on a number of metrics to make sure that their campaigns are in line. Among these is the extremely important ad fill rate[6].

What Is Ad Fill Rate?

The ad fill rate is a measure of performance[1] produced by ad networks. “Fill rate” refers to the percentage of impressions served by an ad network[2]. For example, if an ad network promises 1 million impressions and it has a fill rate of 100%, then all million ads will be displayed. If the impression[3] count is lower than this, then the actual fill rate can be lower than 100%.

This measurement is the percentage of an ad request[4] filled with an advertisement in comparison to the number of ad requests in a given time period. For example: an “80% fill-rate” means that out of 100 ad requests, 80 ads are filled and 20 are not.

Fill rate = (ads served) / (ad requests) x 100

It may not always be true that the number of requests by advertisers and number of requests by publishers are equal.

The numbers may differ due to:

  • Advertisers pausing their campaigns
  • Ads not being approved for running due to violation of publisher[7]’s policy
  • Publisher errors; etc.

100% Fill Rate – Is it Good or Bad?

When it comes to fill rate, a high number is usually better than a low one. However, if the ad network delivers 100% of its inventory[8], but does not deliver any targeted ads, then a publisher will generate no revenue from that ad network. On the other hand, if the ad network delivers 50% of its inventory and those impressions are highly targeted towards a publisher’s audience – revenue can be far greater than what it would otherwise be with 100% fill rate.

The most important thing to remember about fill rates is that they do not tell you anything about your actual earnings. It’s perfectly possible for an ad network with low fill rate to actually provide higher CPMs than another ad network with high Ad Fill Rates.

Average Ad Fill Rate

Ad fill rates can really range from areas of around 20% to 100%. These averages can be deceiving. Networks’ ad fill rates will vary significantly depending on the publisher’s content and traffic. It really depends on the ad network, what they’re offering, and what their priorities are in terms of distribution. If a given network values providing their clients with high CPMs over making sure every ad gets filled, they are likely to have a lower fill rate. On the other hand, a network with a prioritization on distribution rather than match quality may see a 100% fill rate, with the possibility of poorer results.

The size of the network also matters, with more established platforms inevitably being able to offer more outputs and viable options. Fill rate also varies with time, usually dropping during peak times or when ad requests peak.

Why your fill rate isn’t 100%?

Ad networks usually do not guarantee 100% fill rates. It’s extremely rare to see an ad network that guarantees anything higher than 80%, but the actual figure is usually much lower.  As mentioned earlier, the fill rate can vary significantly depending on a large number of factors and is likely to drop during peak times or when ad requests peak.

Since publishers cannot control which ads are shown on their site, they cannot control whether or not their ads will be served, so it is possible for them to click more often than usual. This would result in low earnings due unserved impressions and therefore cause a drop in ad revenue for the publisher.

Ways to Maximize Your Fill Rate

To boost fill rate, employ a greater number of ad networks. It’s probable that another ad network will complete the request if one fails. However, it must be noted that this system doesn’t work 100% of the time. It’s considered to be very risky due to the possibility of falling short on CPMs should one ad network fall short whereas another brings in higher revenue.

One of the most effective ways to optimize your fill rate is by collecting as much data as possible for analysis purposes. Even if one or more Ad Networks are providing good enough rates, some may perform better overall if analyzed correctly. Collecting as much data as possible from your advertisers and publishers will help you to determine which ad networks are performing better overall, and ones that can bring in higher revenue for the lowest price.

Another way is by using different ads each time an ad call[9] fails. If there are multiple advertisers for the same space, then use a different advert from among them. This can help boost your fill rate even though you’re only increasing the number of times you make an ad call.

Another important thing to consider is looking beyond just fill rates. Since increased ad revenue is the goal of all publishers, it’s advised that you focus on increasing your CPMs and not just your fill rates.


Advertising effectiveness can be determined by measuring data related to advertising effect and fulfillment.  This can be done by taking ad fill rates, cost per click[5] (CPC), and conversions into consideration. By analyzing the data, publishers can determine if their ad network is delivering results or if it may be time to switch networks.

Doing this can make it easier to identify ineffective advertising campaigns, and in turn, reduce losses. It also allows for more timely ad changes, resulting in more consumer-centric and outcome-oriented marketing. As a result, improper advertising may be avoided, time and resources may be saved, and overall marketing quality can increase.

1. performance. A form of advertising in which the purchaser pays only when there are measurable results.
2. ad network. A company that serves as a broker between a group of publishers and a group of advertisers by aggregating inventory and audiences from numerous sources in a single buy. Ad networks traditionally aggregate unsold inventory from publishers in order to offer advertisers a consolidated and generally less expensive pool of impressions, but they can have a wide variety of business models and clients. In the context of ad trafficking and ad tech, the term "network" is generally taken to mean an ad network.
3. impression. Impression is when a user views an ad on a page or when an ad is displayed on a webpage.
4. ad request. Ad Request is an action where your website sends a request to your ad server to fill an ad unit with an advertisement. An ad request is made when a user starts loading your webpage/mobile app. The ad request action will happen for every ad unit on a specific webpage. Ad requests can be counted even if no ads were returned/delivered from your advertisers.
5. cost per click. Cost per click. A payment model in which advertisers pay each time a user clicks on their advertisement.

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