Key Takeaways

• Fill rate is the percentage of ad requests that successfully deliver an ad impression

• The formula is: Fill Rate (%) = (Ad Impressions Served ÷ Ad Requests Made) × 100

• Low fill rates directly impact revenue potential and can indicate technical or inventory problems

• Most publishers should aim for fill rates between 70-90% depending on their niche

What Is Fill Rate and Why Should You Care?

If you're running ads on your website or app, you've probaly heard the term "fill rate" thrown around. But what does it actually mean in practice?

Simply put, fill rate measures how often an ad appears when your site or app asks for one. Every time a visitor loads your page, your ad slots send out requests for ads. Sometimes those requests get filled with an actual ad, and sometimes they don't. Your fill rate is just the percentage of successful ad deliveries.

Think of it like this: If you have 100 people walk into your store but only 75 of them buy something, your "sales fill rate" would be 75%. In ad tech, if your site makes 1,000 ad requests but only 800 result in ads being shown, your fill rate is 80%.

How to Calculate Fill Rate

The math here isn't complicated. Take the number of ad impressions actually served, divide by the total number of ad requests made, then multiply by 100 to get a percentage:

For example:

• Your site sent 10,000 ad requests last week

• 7,500 ads were actually displayed

• Your fill rate is (7,500 ÷ 10,000) × 100 = 75%

Most ad platforms will calculate this for you automatically in their reporting dashboards, but understanding the formula helps you make sense of what's happening behind the scenes.

Why Fill Rate Matters for Your Bottom Line

A low fill rate is basically leaving money on the table. Every unfilled ad request represents a missed opportunity to generate revenue. According to research from AdPushup, even a 5% improvement in fill rate can significantly boost overall revenue for publishers.

Beyond the immediate financial impact, fill rate serves as a diagnostic tool. If your fill rate suddenly drops, it could signal problems like:

• Technical issues with your ad implementation

• Low-quality content that advertisers are avoiding

• Poor targeting that doesn't match available demand

• Ad blockers affecting your audience

What's a "Good" Fill Rate?

There's no one-size-fits-all answer, but most publishers should aim for:

Don't obsess over reaching 100%. As IS.com explains, extremely high fill rates might actually indicate you're undervaluing your inventory or not being selective enough about ad quality.

What Affects Your Fill Rate?

Several factors influence how well your ad requests get filled:

1. Geographic Location of Your Audience

Advertisers spend different amounts in different regions. Traffic from the US, UK, and Canada typically has higher fill rates than traffic from developing countries where advertiser demand might be lower.

2. Ad Format and Placement

Some ad formats and placements consistently outperform others. According to Mile.tech, video ads often have lower fill rates than display ads, but they usually command higher CPMs.

3. Device Type

Mobile and desktop can see different fill rates based on:

• Screen size limitations

• Advertiser budgets allocated to each platform

• Technical compatibility issues

4. Time of Day and Seasonality

Fill rates fluctuate throughout the day and year. The advertising industry experiences seasonal peaks (like Q4 holiday season) and valleys (like early January).

5 Practical Ways to Improve Your Fill Rate

1. Implement a fallback strategy: Use waterfall setups that pass unfilled requests to additional demand sources.

2. Optimize page load speed: Faster pages give ad networks more time to respond before users bounce.

3. Test different ad networks: Some networks might have better demand for your particular content niche.

4. Review your ad slots: Sometimes removing poor-performing ad units can improve overall fill rate.

5. Consider audience targeting: Better audience data can make your inventory more attractive to advertisers.

Common Fill Rate Misconceptions

There's a common misunderstanding that higher fill rates always mean more money. But that's not necessarily true. Sometimes it's worth accepting a lower fill rate if it means higher quality ads and better CPMs.

For instance, a site with an 85% fill rate but a $2.00 average CPM might earn more than a site with a 95% fill rate but only a $1.50 CPM.

Don't Isolate Fill Rate from Other Metrics

Fill rate shouldn't be viewed in isolation. As 7SearchPPC notes, it's most valuable when analyzed alongside metrics like:

• eCPM (effective cost per thousand impressions)

• Viewability scores

• User engagement metrics

• Overall revenue

The Bottom Line

Fill rate is a fundamental metric for understanding how effectively you're monetizing your available ad inventory. While you shouldn't obsess over small fluctuations, consistent monitoring helps identify opportunities and troubleshoot problems before they seriously impact your revenue.

By understanding what affects fill rate and implementing strategies to optimize it, publishers can make more informed decisions about their ad stack and monetization approach.