Formats & creative · also called IAB ad units, standard ad sizes, New Ad Portfolio
IAB standard ad sizes
IAB standard ad sizes are the common banner dimensions, such as 300×250, 728×90 and 320×50, recommended by the IAB so one creative fits ad slots across many websites and apps.
Without standard sizes, every advertiser would need a different creative for every site. The IAB's ad unit guidelines solve that by defining shared dimensions. The best-known include the 300×250 medium rectangle, 728×90 leaderboard, 160×600 wide skyscraper, 300×600 half page, 970×250 billboard and, on mobile, the 320×50 banner.
In 2017 the IAB Tech Lab published the New Ad Portfolio, which moved toward flexible, aspect-ratio-based sizes that adapt to screens, and folded in LEAN principles (light, encrypted, AdChoices-supported, non-invasive). Legacy fixed sizes remain the most commonly traded in practice.
Sizes matter for money as well as design. The most common sizes attract the most demand, so they fill better and often earn higher eCPM. Ad slots frequently accept several sizes so more buyers can compete. Unusual sizes may earn less unless sold directly.
Think of it like this
IAB ad sizes are like standard paper sizes (A4, Letter): because everyone agrees on them, a document prints correctly on almost any printer.
An example
A publisher allows both 300×250 and 336×280 in its sidebar slot; adding 300×600 lifts bids by attracting more demand for the larger size.
Related terms
Ad slot (ad unit)
An ad slot (or ad unit) is a specific, defined place on a page, app screen or video stream where an ad can be shown, with its own size, format and rules.
Display advertising
Display advertising is visual online advertising, such as banners, images, animations and rich media, shown in ad slots on websites and apps, as distinct from search, video or audio ads.
Creative
A creative is the actual ad content a person sees or hears, such as an image, video, audio spot, HTML5 animation or native text, delivered into an ad slot.
IAB Tech Lab
IAB Tech Lab is the non-profit standards body for digital advertising technology, founded in 2014, which develops specifications such as OpenRTB, VAST, ads.txt, sellers.json and the Open Measurement SDK.
Sticky ad
A sticky ad is an ad unit that stays fixed on the screen, usually at the top, bottom or side, while the user scrolls through the page content.
Sources: IAB Tech Lab: IAB New Ad Portfolio