Ad Fill Rate – A Beginner’s Guide

Ad Fill Rate – A Beginner’s Guide

You have a website, you’ve monetized it, and you want as much revenue as possible. Every time a user comes to your site is another opportunity. If they are not served ads that’s money not in your pocket. This is where ad fill rate comes in. Understanding this metric will enable you to maximize your revenue.

What is ad fill rate?

Ad fill rate is the percentage of ads served on a site relative to the number of ads requested.

There is a simple formula to calculate your fill rate

Ads served / Ads Requested x 100 = Fill Rate

For example: 100 ads are requested and 90 are served the fill rate is 90%

People often mistakenly believe that if an ad is requested that means it was served and viewable. However, with all the tech involved, there are a few more steps until an ad is seen after it’s been requested. Understanding what happens in those in-between stages can help Publishers understand why their fill-rate may not be what they expected, and what they can do about it.

Average Fill Rate

It’s tricky to pin down an average rate as there are so many moving parts. So, we’ll go through the different factors so you can get a better idea of what’s going on.

First Page Load vs. Refresh

First, it’s important to answer the question of are you considering the first page load or is the refresh included. First page load refers to the ad that appears when a user first comes to the page. Refresh is when a new ad is called without reloading the page. This happens when a user is one a page for a set amount of time, often around 30 seconds. If only considering the first page load, a publisher’s ad fill rate will be significantly higher. The ad refresh often does not serve an additional ad thereby lowering the site’s average rate considerably.

Ad Networks and Ad Partners

Next, understand that most Publishers are connected to either multiple ad networks or Ad Partners (like NMM) who themselves are connected to SSPs and DSPs. Individual networks generally have the capability to fill ad requests 20% to 50% of the time. The only ad network capable of consistent 100% fill is Google AdSense because of their extensive supply. But even they can’t achieve that fill rate for a poor site, with a user located in third-world countries. (Whether you want Adsense set to fill at 100% is another discussion. Short answer is no.)

Most ad networks can only fill 20 to 50% of requests for two reasons, exclusivity and excess supply. Ad networks prefer to work with advertisers and brands that are premium because in turn it makes them more desirable to publishers. The push for premium comes back to brand safety concerns and prestige. Regarding excess supply, there are millions of monetized sites, and many publishers plugging into a single ad network. While there are many ads waiting to be served (Google serves around 30 billion a day) the supply of websites outpaces the availability of quality ads. Therefore, many requests go unfilled due to lack of supply. In turn this affects a site’s fill rate.

Understandably, Publishers do not want to have their ad fill at 20% to 50% because that wouldn’t leave 50% to 80% of their potential revenue on the table. Therefore, most Publishers partner with multiple ad networks. For a more strategic approach, they’ll partner with an Ad Tech partner like Next Millennium. We transact with other SSPs, supplement with direct campaigns, offer ad ops development and support. Additionally, we have long partnerships with SSPs that enable us to optimize the position of the sites we partner with. We also have strong direct partnerships with ad agencies to add additional ad demand that is unavailable on the open market.

Optimizing for fill

Some publishers may try increase their ad fill by adding more ad networks to their stack. That’s not a good idea. Too many ad networks will increase latency, slow down a site, and make users bounce. So how can publishers optimize their fill rate without adding a million ad networks?

Before publishers add other ad networks, they need to understand what their needs are and what features each network offers to increase their fill. The following are a few things to consider

Header Bidding in actionHeader Bidding

This goes without saying, but if you’re not using header bidding, you’re in the Dark Ages. The simple switch will boost your ad fill.


Knowing where your traffic from is vital. If you know your traffic sources, you can partner with ad networks that have ads targeting your traffic’s demographic. For example, if all your traffic is from North America yet all your ad networks are European based advertisers, most of your ads requested are going to be unfilled because the geos do not match the target user.

Flexible Ad Units

Having diverse types of ad units available for advertisers to display on your site gives you more opportunity to receive. If you can only accept one type of ad format that limits the options available. When you’re more flexible, you have more opportunity. Also consider including formats that command higher CPMs like video or if you’re an app, rewards.

Viewable Placements

Advertisers are wary of buying ads at exceptionally low CPMs because they assume the placement is sub-optimal. Making sure that you offer viewable placement can increase your fill rate

What should be your ad fill goal?

People mistakenly believe that 100% Ad fill is the goal. It’s not. Because if your ad fill is 100%, 99% of the time that means that your CPM is probably extremely low and you’re getting so many ads because it’s cheap. In addition, those ads are likely to be of lower quality.

How do you solve for this problem? This is where price floors come in.

What is Price Floor?

Price floor refers to the lowest amount a Publisher is willing to accept for an ad placement. Every publisher should set a price floor.

Price floors can be tricky and counterintuitive. If you set your price floor too high, then you will likely receive a low ad fill because most advertisers aren’t willing to spend that much. Conversely, if you set it too low, it sends a signal to advertisers that your space is not premium or that they can get it at a lower rate. Advertisers may have originally been willing to spend more on your space, but your lower floor indicates you’re lowering your bar, so they will lower their bids. Finding that price balance is a delicate process.

Which brings us to ad fill thresholds.

Ad Fill threshold

Ad fill threshold is the percentage point in which a site finds its balance with the price floor. It’s the point that if the publisher increases its price floor it begins to lose revenue, because advertisers are not willing to spend that much. And if it lowers its price floor it will lose revenue because it’s only receiving lower CPMs.

Ad threshold is fluid and changes often. So even if you think you found a magic number for your site, it’s always wise to check on it. Experiment with it to ensure that it’s still at an optimal rate. NMM‘s algorithm has a dynamic floor pricing that automatically adjusts the floor pricing to optimize a site’s ad fill threshold. This removes the stress of test and tweaking from the publisher.

Other Factors that affect your ad fill rate

And still, with all that planning and tweaking, there are other factors that will affect your ad fill rate.


CPMs are highest in Q4 which has the major holidays. There’s always an ad fill and CPM slump in Q1. It’s not you, it’s the market. Hold tight.

Technical issues

A site may have technical issues preventing ads from displaying, or it may also not be accurately reporting them. It’s important to always run through your tech and ensure it’s not glitchy and is up to speed. A solid ad partner like NMM can help with that.


Latency or more specifically, site speed is a concern when it comes to ad fill. If your site is slow, users may bounce or scroll past ads before they come into view. This will affect your site’s viewability and SERP scores. Keeping up to date and addressing Core Web Vitals issues on your site is vital.

Ad blockers

Around 40% of Internet users use ad blocker. Though the number is significantly lower in the United States (closer to 25%). Depending on how the ad blocker is coded you may or may not see a drop in and fill rate. Some ad blockers stop the ad code from running at all. In that case, ad fill will not be affected. Other’s stop the ad from being viewed, but doesn’t stop the request, in that case the ad fill rate will drop. There are a few things Publishers can do to respond to ad blockers and encourage users to disable them.


Ad fill rate is an interesting metric that has elements both within and out of the Publisher’s control. Publishers should take actions on the elements they can affect change and cross their fingers for the rest.

Learn more about how Next Millennium can help your site.

Esther Kurtz