/fɪl reɪt/

Fill rate is a key metric in digital advertising that measures the percentage of ad requests successfully filled with an actual ad impression. It represents how efficiently a publisher is monetizing available ad inventory and is calculated using the following formula:

Fill Rate = (Ad Impressions / Ad Requests) × 100

For example, if a website sends 100,000 ad requests to an ad server and receives 80,000 ad impressions, the fill rate would be 80%. A high fill rate indicates strong demand for a publisher’s inventory, while a low fill rate suggests unsold ad space due to factors like high price floors, limited demand, or poor ad placement.

Why Fill Rate Matters

For publishers, fill rate is an essential indicator of ad monetization efficiency. A low fill rate means missed revenue opportunities, while a high fill rate suggests effective inventory management. However, a 100% fill rate is not always ideal—it may indicate that the publisher’s price floors are too low, resulting in lower CPMs (Cost-Per-Mille).

The ideal balance is to maximize both fill rate and CPM, ensuring that every impression generates the highest possible revenue.

Factors That Affect Fill Rate

Several factors influence fill rate, making it an important metric to monitor and optimize.

• Demand vs. Supply: If there is strong advertiser demand for a publisher’s inventory, fill rates will be higher. If demand is low, there may be unsold impressions.
• Price Floors: Setting minimum bid requirements (floor prices) that are too high can lead to unfilled impressions if advertisers are unwilling to meet the price.
• Ad Quality & Placement: Poorly placed ads or ad formats that don’t align with demand can negatively impact fill rate.
• Latency & Load Time: If an ad takes too long to load, it may not be served in time, reducing fill rate. Optimizing page speed and ad loading can help improve fill rates.
• Competition Among Demand Sources: Using multiple demand partners, such as ad exchanges, demand-side platforms (DSPs), and header bidding, increases competition and helps improve fill rates.

Publishers need to balance fill rate and CPM to maximize revenue while ensuring high ad quality and user experience.

Fill Rate vs. Ad Refresh Rate

While fill rate measures the percentage of successfully served ads, ad refresh rate refers to how often ad slots reload with new ads. Some publishers use ad refresh strategies to improve monetization by increasing the number of impressions per user session. However, an aggressive ad refresh strategy can negatively impact viewability and user experience.

While both are important, they serve different purposes in ad inventory optimization.

How to Improve Fill Rate

Publishers looking to increase fill rates should focus on optimizing demand and inventory settings:

• Use Header Bidding: Implementing header bidding allows multiple ad networks to compete for impressions in real time, increasing fill rate.
• Adjust Price Floors Strategically: Lowering floor prices slightly can help fill more impressions without drastically reducing CPMs.
• Enable Multiple Demand Sources: Using SSPs, ad exchanges, and programmatic demand ensures more buyers compete for inventory.
• Improve Page Speed & Ad Loading: Faster-loading pages reduce unfilled impressions due to latency issues.

Balancing price and demand is key to maintaining a high fill rate while maximizing revenue.

Fill rate is a crucial metric for publishers looking to optimize their ad revenue. A high fill rate indicates strong demand and efficient inventory monetization, while a low fill rate suggests missed opportunities due to pricing, demand, or technical issues.