Fill Rate

Fill Rate means the number of ad impressions that actually deliver ads out of the times an ad was requested by an ad server. It can be used to measure any situation where an attempt is being made to place ads on the internet, for example:

  • The number of placements on a website that successfully shows ads
  • The amount of times an ad tag successfully delivers an ad to a user
  • The amount of ads an ad network actually provides to a website without having to use default ads

Think of it this way – you put up 100 billboards around town. Your fill rate is the percentage of ads you actually put up on those billboards. It does NOT count as the number of ads you sell, or the number of posters you receive. So even if you sell 100 billboards, if you only have time to put up 95, then your fill rate is 95%.


Fill Rate Formula:

Fill Rate EquationClick to enlarge


Technical Information

You may expect that every ad you want to sell, you can sell in one way or another. This, unfortunately, is not the case with most ad networks, as, for one reason or another, they simply do not have enough ads to fill your site.

This is why most ad networks will allow you to supply them with default ads – so that ads they don’t sell still have a chance of being filled.

Reasons for a less than 100% fill rate can include:

  • Ad setup problems – ads may work on some browsers/computers/operating systems, but not all, and as this is hard to test it will often lead to a low fill rate.
  • Latency – An ad may take so long to load that a user leaves the page before it does so.
  • Reporting discrepancy – the analytics on the site counts an ad impression as soon as the page starts to load, whereas the ad server only counts it once the ad is fully loaded. The time between these two events can be long enough for a user to leave.
  • Ad Blockers – some adblockers stop ad networks instead of ad calls. In these cases, there will be an ad request, but no ad will be able to appear.


Average Fill Rate

It can generally be said that if the fill rate of a network is high, then the eCPM will be low (or at least lower than normal). This is why most ad networks have a fill rate between 20-30%. AdSense is a notable exception to this rule – it has such a large amount of ads available to it, that it generally provides a 100% fill rate.


Fill Rate Advice for Site Owners

To make sure you get as many ads on your site (and therefore as much money as possible), always supply ad networks with default ads. It makes sense in most cases for these to be for AdSense so you can make sure all your inventory is filled.

If you are daisy-chaining ad networks, then you shouldn’t really use more than three ad networks, as the latency can get out of hand.

Note: Do not accept ad networks own measure of fill rate, as they will most likely use the one which is most generous to them. This means they will measure ad requests at the last possible millisecond, and ads being successfully delivered the very moment they start to load.

In reality, this will mean lots of missed ads – so always work out the fill rate by using your own analytics.


Fill Rate Advice for Ad Buyers

If you are using ad tags to deliver rich media ads, then try and keep the K Weight low in order to increase the number of users who will load them before they leave the page. Also beware of using too many analytics services on one set of ads, as they can cause enough latency (or general problems) to stop your ad tags working properly.

Our advice is to make sure you have an analytics provider you trust and use them to monitor your fill rate.

Note: If you notice a sudden dip in your fill rate then there is likely a problem with your ad which needs to be addressed immediately. Similarly keep track of the number of backup gifs you are delivering, as they may mask a decrease in fill rate.


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