Every time your app asks an ad network for an ad, that request either comes back with something to show or comes back empty. Fill rate is the share of those requests that get answered. It is one of the plainest measures of how efficiently a placement turns demand into shown ads, and every empty request is simply missed revenue.

How to calculate fill rate

Fill rate = (Ads served / Ad requests) x 100

Fill rate = (Ads served / Ad requests) x 100

Fill rate = (Ads served / Ad requests) x 100

The result is a percentage. A fill rate of 100 percent means every request returned an ad; anything below that means some share of your requests found no buyer and earned nothing.

A worked example

Say a placement makes 1,000,000 ad requests in a day and 850,000 of them return an ad:

(850,000 / 1,000,000) x 100 = 85% fill rate

(850,000 / 1,000,000) x 100 = 85% fill rate

(850,000 / 1,000,000) x 100 = 85% fill rate

The remaining 150,000 requests went unfilled. Each one was a moment when a user could have seen an ad and did not, which is revenue that never had the chance to exist.

Fill rate and eCPM

Fill rate means little on its own. It has to be read next to eCPM, the earnings per thousand impressions. A placement with a spectacular eCPM that fills only ten percent of the time can earn less than a modest eCPM that fills nearly every request. The number that actually pays you depends on both together, so chasing one while ignoring the other is a quiet way to lose money.

A simple way to see it is to multiply the two. High eCPM and low fill produce a thin trickle of well-paid impressions; moderate eCPM and high fill produce a steady flow of decent ones, and the steady flow often wins on total revenue. This is why raising a price floor to lift eCPM can backfire: the higher price rejects more bids, fill falls, and the placement ends up earning less than before. The best placements hold both numbers high at the same time.

Why fill rate matters

Low fill usually points to a supply problem: too few demand sources bidding, price floors set too high, or a hard-to-monetize audience. Publishers raise it by adding demand through Ad Mediation, which routes each request across many networks, and by tuning the Waterfall so requests cascade to the next buyer when one declines. The goal is to keep as much of your Ad Inventory earning as possible. Fill also swings by geography and format, so the same app can see near-total fill in one market and unanswered requests in another, which is why publishers watch it per segment rather than as one blended figure.

Where offerwalls fit

An offerwall provides dependable, high-value fill from users who are already motivated to engage. Because offers are chosen by the user rather than auctioned in the split second before an impression, they can backfill requests that standard demand leaves empty. RevU adds reliable fill on top of a publisher's existing demand, so requests that would have gone to waste can still return value.

Common mistakes to avoid

• Reading fill rate without eCPM, and celebrating a full placement that barely pays.

• Setting price floors too high, so fill collapses and total revenue falls with it.

• Trusting one blended number, when fill rate varies sharply by geography, format, and network.