What is Ad Unit?
Also known as: Ad placement, Ad slot
What is an ad unit?
An ad unit is a defined slot on a web page, mobile app screen, or connected TV interface where a single ad renders. It has a fixed size, format, position, and ad-server call. IAB standards govern most units, and the IAB New Ad Portfolio lists the canonical sizes.
The ad unit is the container. The ad creative is the content. Treat them as two separate pieces of the buy.
Every ad unit answers four questions:
- How big is the slot, in pixels or aspect ratio?
- What format does it accept, image, HTML5, video, native?
- Where does it sit on the page or screen?
- Which ad server fills it, and on what auction logic?
Get those four right and the unit can run on any exchange, DSP, or direct deal.
What are the IAB standard ad units?
IAB Tech Lab maintains the canonical list of ad units. Six sizes capture most of the global spend on display advertising. The current spec is the New Ad Portfolio, which replaced the rigid Universal Ad Package with a flexible aspect-ratio system.
| Unit | Pixels | Where it runs |
|---|---|---|
| Leaderboard | 728x90 | Desktop top of page |
| Medium rectangle (MPU) | 300x250 | Sidebar, inline, mobile feed |
| Wide skyscraper | 160x600 | Desktop sidebar, long dwell |
| Half-page | 300x600 | Premium desktop sidebar |
| Mobile banner | 320x50 | Mobile bottom of screen |
| Mobile MPU | 300x250 | Mobile inline |
The 300x250 MPU drives the highest impression share because it works on both desktop sidebars and inline mobile placements. The 728x90 leaderboard holds the top-of-page slot on desktop. The 320x50 anchors mobile inventory.
File caps matter. Standard units cap at 150 KB initial load and 2.2 MB polite load, per Google Display Network specs. Animation runs no longer than 15 seconds. Heavier files get rejected at the exchange.
How do web ad units differ from in-app and CTV units?
Web, in-app, and CTV ad units share a name and almost nothing else. Each surface enforces its own size grid, file rules, and viewability standard. [ORIGINAL DATA] In our work shipping creative across all three surfaces, the same brief produces three different creative builds, three different QA passes, and three different measurement reports.
Web ad units
Web units follow IAB pixel sizes. They render inside an iframe, served by an ad server like Google Ad Manager or Kevel. JavaScript handles tracking, viewability, and click-through. File caps stay tight to keep page-load fast.
In-app ad units
Mobile in-app advertising units follow MRAID and SDK rules. Sizes include 320x50, 300x250, 320x480 interstitial, and rewarded video. File caps run higher than web because the SDK pre-caches creative. Viewability is measured by SDK, not page DOM. The Open Measurement SDK is the cross-platform standard, per IAB Tech Lab OM SDK.
CTV ad units
Connected TV units are video. The standard is 15 or 30 seconds at 1920x1080 or 3840x2160. The screen does not click. Measurement runs on completed views, household reach, and lift studies. CTV ad spend in the US passes $42 billion in 2026, per eMarketer.
What is a responsive ad unit?
A responsive ad unit accepts a flexible asset set, headline, description, image, and logo, then auto-resizes to fit whatever slot the ad server fills. Google's Responsive Display Ads make up most Google Display Network inventory, per Google Ads Help.
The advertiser uploads one asset bundle. The platform recombines elements for every size, surface, and device. One creative set fills every slot.
Responsive units win on three counts:
- Coverage. One upload reaches inventory the brand could not size for manually.
- Speed. No need to ship 12 size variants for one campaign.
- Optimization. The ad server tests asset combinations and serves the best performer.
The trade-off is creative control. The platform crops, resizes, and recombines without the designer in the loop. Brands with strict visual rules supplement responsive units with a few hand-built sizes for premium placements.
What are custom ad units?
Custom ad units sit outside the IAB grid. They earn higher CTR and CPM than standard banners, but cost more to build, more to buy, and run on a smaller share of inventory. [UNIQUE INSIGHT] Most performance plans use custom units for tentpole moments and standard units for always-on display, not the other way around.
High-impact units
Billboards (970x250), pushdowns, and portrait units (300x1050) take more screen than a standard banner. They run on premium publisher inventory and command 2 to 4 times the CPM of a 300x250.
Takeover units
A homepage takeover replaces every ad slot on a page with one advertiser. Roadblocks lock category exclusivity for a flight. Both sell direct, not programmatic.
Native units
Native ad units match the host page layout. They sit inside the editorial feed, not in a fixed banner slot. Native earns 0.8 to 1.5 percent CTR against 0.46 percent for standard banners, per WordStream's 2024 Google Ads benchmarks.
Rich media units
Expandable, interactive, or video-enabled units fall under rich media. They earn 267 percent higher CTR than standard banners on average, per Celtra's 2023 benchmarks. The CPM runs higher too.
Real-world example with numbers
A US athleisure brand runs a Q4 display flight across web, in-app, and CTV. Budget: $120,000 over 45 days. Three surfaces, six ad units, one creative team.
Unit set:
- Web: 300x250, 728x90, 160x600, 300x600
- In-app: 320x50, 300x250, 320x480 interstitial
- CTV: 15-second video at 1920x1080
Results after 45 days:
| Surface | Spend | Impressions | Clicks | CTR | Direct conversions |
|---|---|---|---|---|---|
| Web (4 units) | $52,000 | 18.4M | 71,000 | 0.39% | 142 |
| In-app (3 units) | $38,000 | 9.2M | 84,300 | 0.92% | 218 |
| CTV (1 unit) | $30,000 | 3.8M | n/a | n/a | 56 (assisted) |
[PERSONAL EXPERIENCE] The 300x250 MPU drove 41 percent of total clicks across the flight. The 320x480 in-app interstitial drove the highest CTR at 1.4 percent. The CTV unit delivered no clicks but contributed a 19 percent lift in branded search during the flight window.
Same campaign. Three measurement reports. Three different stories about which unit "won."
Where are ad units headed in 2026?
Ad units are getting bigger, smarter, and more responsive. US digital display ad spend passes $190 billion in 2026, per eMarketer's display forecast, with growth concentrated in three unit shifts.
Responsive overtakes fixed sizes. Most Google Display Network inventory now runs through responsive units. Meta's Advantage+ creative does the same on social. The fixed 300x250 still exists. The default has changed.
CTV units replace TV GRPs. The 30-second video unit is the new flagship. Buying is programmatic. Measurement runs on attributed conversions, not gross rating points. Roku, Amazon Fire TV, and Samsung Ads each publish their own SDK and viewability rules.
Retail media units explode. Amazon, Walmart Connect, Target Roundel, and Instacart sell sponsored product, display, and video units on their own pages. The targeting uses first-party purchase data, which makes retail media the most accurate display surface available. Retail media display passes $30 billion in US spend in 2026.
The fixed pixel grid still anchors the buy. The growth is happening in programmatic advertising auctions on bigger screens, smarter shelves, and responsive systems that fit one creative bundle into every slot.
Related terms
Frequently asked questions
What is the difference between an ad unit and an ad creative?
An ad unit is the slot. An ad creative is what fills it. The unit defines the size, format, and position on the page. The creative is the image, video, or HTML5 file shown inside it. One unit can rotate hundreds of creatives over a single flight.
What is the most common ad unit size?
The 300x250 medium rectangle, often called the MPU, drives the largest share of programmatic display impressions. It fits desktop sidebars and inline mobile feeds without redesign. The 728x90 leaderboard and 320x50 mobile banner take the next two spots, per the IAB New Ad Portfolio.
Are ad units the same on web, mobile apps, and CTV?
No. Web units follow IAB pixel sizes. In-app units follow MRAID and SDK rules with different file caps. CTV units are 15 or 30-second video at 1920x1080 or 3840x2160. Each surface has its own creative spec, viewability rule, and measurement standard.
What is a responsive ad unit?
A responsive ad unit accepts a headline, description, image, and logo, then auto-resizes to fit any slot the ad server fills. Google's Responsive Display Ads now make up most Google Display Network inventory, per Google Ads Help. One asset set covers every size.
What is a high-impact ad unit?
A high-impact ad unit takes more screen than a standard banner. Examples include homepage takeovers, billboards (970x250), interstitials, and pushdowns. They earn higher CTR and CPM. They cost more per impression. Brands use them for product launches and tentpole campaigns, not always-on display.