Banner.format

Array of Format objects listing every size the slot accepts, or flexible size ratios. Added in OpenRTB 2.4 and marked recommended from 2.5.

Currentobject arrayRecommendedSince 2.4

Field facts

Path: imp.banner.format, imp.audio.companionad.format, imp.video.companionad.format
Object: Banner
Type: object array
Requirement: Recommended
Added: OpenRTB 2.4
Spec section: 3.2.6

How it is used

The bid states the size it chose in Bid.w and Bid.h, or in Bid.wratio and Bid.hratio for a flex ad. If the request also carries Banner.w and Banner.h, keep them equal to one of the listed formats so every buyer sees the same offer.

Example

Where the field sits in a payload, with everything else left out:

{
  "id": "req-1",
  "imp": [
    {
      "banner": {
        "format": [
          {
            "w": 300,
            "h": 250
          },
          {
            "w": 300,
            "h": 600
          }
        ]
      }
    }
  ]
}

Common mistakes

Copying Prebid.js ad unit sizes verbatim, such as [[300, 250]], instead of objects like {"w": 300, "h": 250}.
Sending sizes as strings such as "300x250"; a Format needs integer w and h fields.
Sending a single Format object instead of an array.

Version history

Added in OpenRTB 2.4, and present in the latest snapshot. The table shows how each version's spec text types the field.

Versions	Type in the spec	Required	Deprecated
2.4	object array	No	No
2.5 to 2.6-202606	object array	Recommended	No