What is bid multiplier?
A bid multiplier is a factor a DSP applies to a base bid to raise or lower it for a slice of traffic, for example 1.2 for a valuable audience or 0.5 for a weak placement. It is buyer-side configuration, not an OpenRTB field. People often confuse it with the impression multiplier in Qty.multiplier, which says how many impressions one digital out-of-home play counts as.
Also called: bid modifier, bid adjustment, bid adjuster.
How it works
Bid multipliers live inside the bidder. A campaign sets a base CPM plus rules keyed on request signals such as Device.devicetype, Device.geo, Imp.instl, or the presence of a user ID, and the bidder multiplies the base bid by each matching factor before any shading. Nothing in the bid response reveals which multipliers applied; the exchange sees only Bid.price.
The OpenRTB multiplier is a different thing. In digital out-of-home one ad play is seen by many people, so Imp.qty carries Qty.multiplier, the number of impressions the play counts as, with Qty.sourcetype and Qty.vendor saying who measured it. The bid stays a CPM per impression, so the cost of one play is the price times the multiplier, divided by 1,000. After the auction the exchange can confirm the quantity won through the ${AUCTION_MULTIPLIER} macro, which should never exceed the value sent in the request.
Mixing the two causes billing errors. A buyer that treats Qty.multiplier as a bid adjustment, or ignores it and books each DOOH win as one impression, misstates both spend and delivery. Read the multiplier as quantity, apply your own modifiers to the per-impression price, and reconcile against ${AUCTION_MULTIPLIER}.
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Related terms
Every term is in the glossary.