Floor Price (Ad Auctions)

A floor price, also called a reserve price, is the minimum bid a publisher or its supply-side platform will accept for a given ad impression. Any bid below the floor is automatically rejected before the auction even compares bidders against each other, regardless of demand elsewhere in the auction.

How floor prices work#

A publisher sets a floor, usually per placement, per ad format, or even per audience segment, inside its ad server or SSP. When a bid request goes out through real-time bidding, every incoming bid gets compared against that floor first. Bids that clear it enter the actual auction; bids that don't are dropped, and if no bid clears the floor at all, the impression goes unsold, either passed to a lower-priority demand source or left unfilled.

With header bidding, where several exchanges compete for the same impression at once, floors get more complicated. A publisher can set a single unified floor across all demand sources or set different floors per exchange or per negotiated deal ID, sometimes using dynamic floor-pricing tools that adjust the floor in near real time based on modeled demand for that specific impression.

Why publishers set floors#

The obvious reason is protecting RPM: a floor stops a publisher from selling an impression for less than it's worth just because demand happened to be thin at that exact moment. Floors also protect private marketplace and preferred deal buyers, who negotiated a specific price, from being undercut by lower open-auction bids for the same inventory.

The tradeoff is fill. Set a floor too high relative to actual demand, and the publisher trades revenue per impression for unsold inventory, since unfilled impressions earn nothing at all. Getting the floor right is a constant balancing act, and most publishers running programmatic at scale revisit floors regularly rather than setting them once and leaving them.

Floors from the buyer's side#

For a media buyer, a floor is invisible until you're consistently losing an auction. If your bids keep failing on a specific placement even when you believe you're bidding competitively, an unpublished floor above your bid is one of the first things to rule out, alongside checking whether a negotiated deal or PMP is soaking up the good inventory before it ever reaches the open exchange. Watching what competitors are actually winning and running, rather than guessing at floor mechanics from the outside, is where a tool like OpenAdLibrary's native ad spy tool is more useful than trying to reverse-engineer auction dynamics from bid logs alone.

FAQ#

Is a floor price the same as a reserve price?

Yes, the terms are used interchangeably in most ad tech contexts. Both mean the minimum bid a seller will accept before an impression is even considered sold.

What happens if no bid clears the floor?

The impression goes unfilled by that demand source. Depending on the publisher's setup, it may pass to a secondary or lower-priority demand path, or simply not render an ad at all.

Can floor prices change in real time?

Yes. Many SSPs offer dynamic floor pricing that adjusts the floor per impression based on modeled demand, device, geography, or time of day, rather than using one static number for a whole placement.

Do floor prices affect fill rate?

Directly. A higher floor rejects more bids outright, which lowers overall fill rate if demand doesn't rise to meet it. Publishers have to weigh higher revenue per filled impression against the risk of more unsold inventory.