What is Fill Rate in Online Advertising?

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When using Propeller Ads to further increase the revenue of your website, understanding fill rate and its importance will give you a better understanding of how our ad network operates and how much you can earn.

In this article, we break down the definition of fill and internal and external factors that affect it.

What is fill rate?

Fill rate is the percentage of ads served based on the total number of page impressions. For example, if you receive 1,000 page impressions where an ad-unit has been placed, and a total of 900 adverts were served per 1,000 impressions, your fill rate would be 90%.

Ads severed / total number of add opportunities = fill rate

A high fill rate generally increases a website’s eCPM and earning potential. As an online marketer, you should strive to obtain the highest fill rate possible.

How do I achieve a 100% fill rate?

It’s pretty much impossible to maintain a 100% fill rate, even if you do everything right. Webpages timing out, visitors leaving before the advert has had time to load, or network issues between you and the ad network can result in ads not being served.

There are a number of variables that affect a website’s fill rate, some of which you can control while others are out of your hands. These will be explained later in the article.

What is the industry standard fill rate?

The best way boost your website’s fill rate is to use a reputable advertising network that has a good reputation and a wide selection of publishers. Most ad networks promise a fill rate of 25-50% which is very low and extremely difficult to monetise.

This is usually because they have few publishers and too many advertisers. As a result, they create too much demand (advertisers) and not enough supply (publishers), which end up giving you the advertiser a low fill rate.

Propeller Ads offers all advertisers a near 100% fill rate (we can’t help website timeouts or visitors leaving before an advert is served), and have an enormous ad inventory to alway fill demand.

External factors that affect fill rate.

There are a number of factors outside your control that affect fill rate, they include:

Location of traffic – Our publishers place specific targeting options on their advertising campaigns to ensure they are shown to relevant prospects. For example, you may receive a website visitor from Ghana, but if no publishers are targeting prospects from Ghana, there could be a chance that no ad will be served.In March 2015, the United States, New Zealand and England topped the list of popular countries publishers target according to Tip List Tips:

Device type – On average, publishers are more likely to serve adverts to users on a mobile device than desktop (and pay more too). Website visitors who use a Blackberry or Windows smartphone may be served fewer ads than traffic using iOS or Android platform, quite simply because they are less popular devices:
Source: Market Realist

You have no control over which devices traffic use to access your site, and publishers often target ads on more popular devices and web browsers.

Advertising networks – There are a number of advertising networks to pick from, with many having just a few publishers and campaigns. With few clients and limited daily budgets, smaller networks don’t have a large enough ad inventory to serve ads resulting in very low fill rates.

Internal factors that affect fill rate

There are a number of things you can do to increase your fill rate, they include:

Optimising website response times – To serve an advert, your website needs to send a request to the ad network with the visitor’s details for them to then serve the appropriate advert.

An optimised website speeds this process up and serves the advert before the visitor has clicked on a new page or left. There are a number of ways to improve the response time of a website from picking a great hosting plan, choosing the right theme and speeding up a website’s load time.

Ad blocking – Fill rate doesn’t take into account ad blocking software and can sometimes misrepresent your actual eCPM and fill rate. For example, if 50% of your traffic use ad blocking software, your fill rate may be close to 100% but your eCPM will be very low.

If you’ve experienced this in the past, it’s either because you picked an advertising network that don’t pay advertisers accordingly or your traffic were using ad blocking software. To ensure ads are served and seen by traffic, use a program like Page Fair to combat against ad blockers.

Use common size ad-units – Placing the most frequently used banner ads by publishers increases your fill rate as there is more demand for such sizes. Typically, the most effective banner ads used by Propeller Ads publishers are:

  • 300×250 (large rectangle)
  • 728×90 (leaderboard)
  • 468×60 (small leaderboard)
  • 160×600 (horizontal leaderboard)

We have optimised all our ad-unit sizes to provide publishers and advertisers the best possible rate of return. You can learn more about ad-units and where to place them by reading our ad-unit best practices guide.

Using multiple Ad slots – Publishers often use a number of different ad sizes to get the most out of their campaigns. To maximise your fill rate and overall revenue, we recommend using a balanced banner selection. For example, if you place three large rectangle ad-units on your website, depending on ad inventory, only two of the three ad-units will serve ads (67% fill rate).

If you use one large rectangle, a small and large leaderboard, you potentially increase your fill rate to 100% as publishers often use multiple ad-units for their ad campaigns. This also provides users with a better ad experience than showing them the same ad over and over again.


When monetising a website using an advertising network, understanding fill rate is very important to find out your rate of return. The two biggest factors to increase fill rate and eCPM is to use an ad blocker and select a reputable advertising network that can guarantee a high fill rate.

Propeller Ads has one of the largest ad inventories in the world and continually provides publishers and advertisers with fill rates that are way beyond the industry standard. Signup today for free and start earning money!


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