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.