The sizes that still carry display
The IAB's flexible ad portfolio exists, but media plans still run on fixed sizes: the 300x250 medium rectangle, 728x90 leaderboard, 300x600 half page, 160x600 wide skyscraper, 320x50 mobile banner and 970x250 billboard, often with 320x100 and 336x280 added. The shapes range from almost square to an eight-to-one strip, so one layout cannot simply be scaled. Group the sizes by shape (horizontal, vertical, rectangle), design a layout for each group, then fine-tune every size. A key visual built with an extendable background and a compact hero makes this far easier.
Legible at tiny sizes
A 320x50 banner holds a logo, about five words and a button, and it is seen at arm's length on a phone. Write the smallest size first, then expand. Use one message per banner, a sturdy typeface, text as large as the space allows and contrast of at least 4.5:1 against the background, the WCAG threshold for normal text. Avoid thin serifs, script faces and text over detailed imagery. Generated imagery tends to be busy, so simplify what sits behind the text and crop tighter on the product, which must stay recognisable at a few dozen pixels tall.
Static or HTML5, and the file-weight caps
Static JPG, PNG or GIF banners are the lightest and most widely accepted. HTML5 banners allow animation, live data from a product feed and interaction, but they need a clickTag for click tracking, a static backup image, and discipline to stay within each publisher's weight limit; IAB guidance sets the initial load from 50 KB for a 320x50 to 250 KB for a 970x250. Google Ads caps uploaded image ads at 150 KB and requires animation to stop within 30 seconds. Generated images are large by default, so export and compress each size deliberately rather than shrinking one heavy master, and keep text as live HTML where the format allows.
Versioning at scale
Sizes multiply with messages, markets and audiences: six sizes, four messages and ten markets is already 240 files before any testing. Treat that matrix as a system. Fix a naming convention that encodes size, market, message and version, keep one source per layout group, and review a contact sheet of every size in every language, because German headlines and Finnish product names are where layouts break. Synthetic White generates the full set from one brief with the brand hub's logo, colours, typography and banned words enforced at generation, and approvals run on the whole set with sign-off and an audit trail.
Updated 25 September 2026