What is fill rate?
Fill rate is the share of a publisher's ad requests that end with an ad served, calculated as filled impressions divided by ad requests. It is a sell-side metric that an SSP or ad server reports per placement, deal, or demand partner. Low fill means bidders saw the inventory and passed, or that their bids were filtered out before any could win.
Also called: ad fill rate, fill.
How it works
Fill sits at the end of a chain of smaller rates. Of the requests an SSP sends, some get bids, some of those bids clear the floor and pass blocks, one wins, and the winner then has to render and be counted. A drop at any step lowers fill, so the useful question is which step lost the impression. Floor rejections (loss reason 100), creative filtering (loss reasons 200 to 215), and render failures each point at a different owner.
Several OpenRTB problems show up as low fill without any error. Floors in Imp.bidfloor above what buyers will pay, video requests that send only the deprecated Video.placement without Video.plcmt, missing or contradictory privacy signals in BidRequest.regs, and a BidRequest.tmax too tight for the supply path all reduce bids at the source. Validating one real request is usually faster than reading dashboards.
Fill rate is not revenue. A publisher can raise fill by lowering floors and still earn less per thousand requests, and a higher floor can cut fill while raising revenue. Read fill next to eCPM or revenue per thousand ad requests, never on its own.
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Related terms
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