What Is a Companion Ad?
A companion ad is a static or interactive display unit that runs alongside a primary video ad, typically appearing in the surrounding page or player interface while the video plays. Its function is to extend brand exposure beyond the video unit itself, giving viewers a clickable touchpoint that persists after the main creative has ended.
The IAB’s VAST (Video Ad Serving Template) and VPAID standards define how video players request and render both the primary video and its associated companion units simultaneously.
How Companion Ads Work
When a publisher’s video player fires an ad request, the ad server returns a VAST response. That response may contain one or more companion ad definitions in addition to the main video creative. The player renders the video in its primary unit while injecting the companion into a designated slot on the page, often a 300×250 or 728×90 banner zone adjacent to the player.
The companion ad loads at the same time as the video and remains visible throughout playback. Depending on the publisher’s configuration, it may persist on the page even after the video finishes, giving it a longer effective impression window than the video itself.
This pairing is coordinated through the VAST <CompanionAds> node, which specifies dimensions, creative assets, and click-through URLs for each companion unit in the response.
Common Companion Ad Formats
| Format | Dimensions | Typical Placement |
|---|---|---|
| Medium Rectangle | 300×250 | Sidebar or below player |
| Leaderboard | 728×90 | Above or below player |
| Wide Skyscraper | 160×600 | Right rail |
| Billboard | 970×250 | Full-width above fold |
| Skin / Roadblock | Custom | Full page surround |
The 300×250 medium rectangle remains the most widely supported companion format across publishers because it fits standard sidebar inventory and is compatible with most video player configurations.
Why Companion Ads Matter for Campaign Performance
Video ads, including pre-roll ads, are time-bounded. A 15-second pre-roll disappears the moment it ends. A companion ad solves this by anchoring a brand message to the page for the full duration of the user’s session on that content.
Research published by the IAB found that campaigns using companion ads alongside video units saw brand recall lift of 20 to 30 percent compared to standalone video placements. The persistent visual presence reinforces the message that the viewer may have half-watched or skipped.
Companion ads also provide a direct response mechanism when the video itself does not. A user who watches a video ad passively can still click the companion unit to visit a product page, claim an offer, or learn more, without needing to interact with the video player directly.
Companion Ad Click-Through Rate Benchmarks
Click-through rates for companion ads run lower than standalone display advertising in isolation, because users are primarily focused on the video content. Industry benchmarks from DoubleVerify and Google Campaign Manager place companion ad CTR between 0.1% and 0.3% for standard formats, with rich media and animated companions reaching up to 0.5% in high-engagement environments.
The relevant metric for most companion campaigns is not CTR alone but combined video-plus-display viewability and brand lift. Advertisers running awareness campaigns weight view-through attribution and recall studies more heavily than clicks.
Simple Companion Ad Efficiency Formula
To evaluate the incremental value of adding a companion unit to a video buy:
Companion Incremental CPM = (Total Campaign Cost ÷ Total Impressions Including Companion) − Base Video CPM
If a video buy costs $25 CPM and the publisher charges an additional $3 CPM to serve a companion unit, the effective incremental reach cost is $3 per 1,000 additional paired impressions. Given that companion units often share the same user session and extend dwell time, this cost is typically justified in upper-funnel campaigns.
Real-World Usage: How Brands Deploy Companion Ads
Ford Motor Company has used companion ads in connected TV and desktop video campaigns to display vehicle configuration tools alongside in-stream video spots. While the 30-second video showcases the vehicle in motion, the companion unit renders a clickable 300×250 with a “Build & Price” call to action, giving engaged viewers a direct path to the configurator without interrupting the viewing experience.
Pharmaceutical brands operating under FDA fair balance requirements frequently use companion ads to display required safety information that cannot be compressed into a short video. The companion carries the full prescribing summary while the video delivers the emotional brand message.
Streaming platforms including Peacock and Paramount+ have reported that advertisers using companion units alongside their video inventory see 18 to 24 percent higher website visit rates compared to video-only placements, based on publisher-reported attribution data.
Companion Ads in Programmatic Environments
In programmatic advertising, buyers negotiate companion ads as part of a video deal package. This can happen through a private marketplace deal or via open auction bidding on video inventory that supports companion rendering. Not all programmatic video supply supports companions. Eligibility depends on whether the publisher has designated companion zones in their ad stack and whether their player passes companion dimensions in the VAST request.
Buyers using Google Display & Video 360 can specify companion creative assets at the line item level. The system will then serve them only to eligible placements that return a matching companion zone in the VAST response. The system silently discards unmatched companion requests rather than generating errors, which means campaign reports should include companion serve rate as a distinct metric from video impression delivery.
Companion Ads vs. Overlay Ads
Companion ads should not be confused with overlay ads, which render inside the video player frame rather than in a separate page zone. Overlays interrupt or partially obscure the video content, while companion ads coexist with it in separate inventory. Viewability measurement for the two formats also differs: companion viewability follows standard display measurement (50% of pixels in view for one second), while video overlay viewability is measured against the video player dimensions.
Frequently Asked Questions
What is a companion ad in digital advertising?
A companion ad is a display unit that runs alongside a video ad, occupying adjacent page inventory while the video plays. It is defined in the VAST response from the ad server and gives advertisers a persistent branded touchpoint that can remain visible after the video ends.
What is the standard size for a companion ad?
The 300×250 medium rectangle is the most widely supported companion ad size across publishers. Other common formats include the 728×90 leaderboard, 160×600 wide skyscraper, and 970×250 billboard, though availability depends on the publisher’s designated companion zones.
What click-through rate should I expect from companion ads?
Companion ad CTR typically falls between 0.1% and 0.3% for standard formats, according to benchmarks from DoubleVerify and Google Campaign Manager. Rich media and animated units can reach up to 0.5% in high-engagement environments. Awareness-focused campaigns should prioritize brand lift and viewability over click metrics.
How are companion ads different from overlay ads?
Companion ads appear in a separate page zone outside the video player, while overlay ads render inside the player frame and partially obscure the video. The two formats use different viewability measurement standards and serve different creative purposes.
Do all programmatic video buys support companion ads?
No. Companion ad support in programmatic depends on whether the publisher has designated companion zones in their player configuration and whether those dimensions are passed in the VAST request. Buyers should monitor companion serve rate as a separate metric from video impression delivery to confirm the unit is actually rendering.
Key Takeaways
- Companion ads extend a video campaign’s message by occupying adjacent display inventory during and after playback.
- They are defined in VAST responses and require publishers to designate companion zones in their player configuration.
- The 300×250 medium rectangle is the most universally supported companion format.
- CTR benchmarks range from 0.1% to 0.5%, but awareness-focused campaigns should prioritize brand lift and viewability over click metrics.
- Programmatic buyers should monitor companion serve rate separately from video impression delivery, as not all video supply supports companion rendering.
For related concepts, see pre-roll ad, display advertising, programmatic advertising, and viewability.