What Is Fill Rate?
Fill rate measures what share of a publisher's ad requests were actually filled with an ad, rather than returning empty. It's a core supply-side health metric — low fill rate leaves inventory unsold even when audience demand exists, representing lost potential revenue.
Fill rate is usually tracked alongside eCPM, since the two together — not fill rate alone — determine total realized revenue from available inventory.
Fill Rate Formula
Divide ads served by total ad requests, then multiply by 100.
Fill Rate = (Ads Served ÷ Ad Requests) × 100
Worked Example
A publisher sends 200,000 ad requests and 176,000 are filled with an ad.
Fill Rate = (176,000 ÷ 200,000) × 100 = 88%
What Affects Fill Rate?
- Price floors — a floor set above what demand is willing to pay directly lowers fill rate on that inventory.
- Demand partner count — more connected exchanges and advertisers generally raises the chance any given request gets a bid.
- Geography and audience — less commercially attractive traffic typically sees lower fill rate from the same demand sources.
- Ad blockers and timeouts — technical factors unrelated to demand can also prevent a request from being filled.
Fill Rate Calculator FAQ
How is fill rate calculated?
Fill rate is calculated by dividing ads served by total ad requests, then multiplying by 100: Fill Rate = (Ads Served ÷ Ad Requests) × 100. Enter your figures above to calculate it instantly.
Why would an ad request not get filled?
Low advertiser demand for that specific impression (geography, audience, time of day), a floor price set above what any bidder offered, technical timeouts, or ad blockers preventing the ad from loading can all cause an unfilled request.
What's a good fill rate?
It varies by inventory quality, geography, and demand partners — fill rate in the 80-95%+ range is common for well-connected programmatic setups, but there's no single universal target. A low fill rate paired with a high CPM on filled impressions can still produce reasonable total revenue.
How does fill rate relate to total revenue?
Revenue depends on both fill rate and the price of filled impressions — raising a price floor can increase per-impression revenue while lowering fill rate, and the net effect on total revenue isn't always obvious without checking both numbers together.