Ad Fill Rate Explained
Fill rate measures the percentage of eligible ad requests that return an ad.
Formula
Filled requests divided by total ad requests, multiplied by 100.
Why it changes
Demand, pricing rules, targeting, geography, device type and technical issues can all affect fill.
Why 100% is not always optimal
Maximizing fill alone does not necessarily maximize total revenue or user experience.
Practical takeaway
Use the metric that matches the business question you are trying to answer. When several metrics describe different stages of the same workflow, compare them together rather than optimizing one in isolation.
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