We can define fill rate as simply the number of times an advertisement is shown at a particular ad space divided by the total number of times an advertisement can be shown at that space. Let’s say there were 1000 opportunities to show an ad for a particular space and only 500 were shown then the fill rate would be 500/1000 which is multiplied by 100 to account for a percentage figure and the resulting answer is 50 percent.
One particular question here might be that why would there be the case that the space is not filled every single time an ad can be shown. Well the answer here is simply that advertisers who bid for spaces to show their ad may not be interested in pursuing that space. This may be because they have already shown the ad to each unique visitor to that space or they are not interested due to a target market/volume mismatch. To have a plethora of advertising demand to ensure maximum fill rates possible the best solution is to work with as many relevant ad-networks and supply side platform as one can.
From the perspective of a developer/owner of a game it is important to create a strategy whereby not only can an advertisement be shown as many times as possible in the spaces he or she offers but that yield/return in terms of revenue is also significant. A high fill rate and competitive CPM rates allow the publisher to earn more. Keeping these factors in mind would assist in maximising the potential of any space.