What is Fill Rate?

Fill Rate is Sell Side specific metric which represents the percentage of ads served based on the total number of page impressions available.

The Fill Rate formula is represented by ;

(Paid impressions / Total impressions served) x 100 = Fill rate %


Your website had 500,000 total impressions or “ad calls” for a given period. Only 475,000 of those impressions returned a paid advertisement:

(485,000 / 500,000 ) x 100 = 97% fill rate

Price Floor, network errors, internet congestion, timeouts and users leaving a web page before the ad is delivered to the page all contribute to why a perfect 100% fill rate rarely happens.