Display advertising has dozens of defined sizes and a handful that matter. The medium rectangle at 300 by 250 and the leaderboard at 728 by 90 have been standard since the early 2000s, and they still account for a large share of available inventory.
That persistence is not inertia for its own sake. Publishers built page templates around those slots, and a size with no slot to sit in has nowhere to be shown however well designed it is.
Which sizes should a campaign cover?
Five will reach almost everything.
| Size | Name | Where it sits |
|---|---|---|
| 300 × 250 | medium rectangle | in or beside content |
| 728 × 90 | leaderboard | above content, desktop |
| 160 × 600 | wide skyscraper | page margin |
| 300 × 600 | half page | margin, high impact |
| 320 × 50 | mobile leaderboard | pinned on phones |
The medium rectangle is the one to produce first if you produce only one. It fits in a sidebar and inside an article, it works on desktop and mobile layouts, and it is the most widely available slot there is.
The half page is the newer addition and the highest impact of the five, because it occupies a large share of the visible screen without needing a redesign around it.
Why are the dimensions so specific?
Because they were standardised so that one creative would fit any publisher. Before that, every site defined its own slots and an advertiser had to produce a bespoke file for each one, which made buying across many sites impractical.
The industry has since moved towards flexible units defined by aspect ratio rather than exact pixels, which suits responsive layouts far better. The fixed sizes did not go away, because the pages built around them did not.
In practice both exist side by side. Producing the classic sizes covers the existing inventory, and a flexible design covers what came after.
What constrains the file itself?
Weight, mostly. Display formats carry a size budget measured in tens or low hundreds of kilobytes, and an ad that exceeds it is rejected rather than shown slowly.
That budget is why most display advertising is flat colour and type rather than photography. A photograph compressed to fit tends to look worse than a designed graphic that never needed the detail.
Animation adds a duration limit and a rule about where it stops. The convention is that motion runs for a few seconds and settles on a final frame carrying the message, because the frame at rest is what most viewers actually see.
What has to be in the frame?
A logo, one clear message, and something that looks like a button. At the smallest sizes there is room for two of those, which is why the mobile leaderboard is the hardest of the set to design.
The button is the part that gets cut when space runs short and it should not be. A clearly marked action outperforms a clever line, and the border of the ad matters too — an ad without a visible edge blends into the page and reads as content rather than as an offer.
Text has to be legible at actual size, which is smaller than it looks in a design tool at 200 per cent zoom. Viewing the export at its real pixel dimensions is the only test that counts.
Why preview before uploading?
Because an ad is judged in context and designed in isolation. A creative that looks balanced on a white artboard can vanish on a dark page or clash with the content around it.
Social ad formats add a second reason: the platform composes the ad from parts. Headline, body text and image are separate fields assembled into a layout, and the assembly truncates text at lengths you cannot see until you preview it.
The carousel format compounds it, since each card is composed the same way and the set has to work as a sequence. Previewing the assembled result catches a truncated headline before a review does.
Where do the sizes go on a page?
Above the fold and beside the content, in that order of value. A slot visible without scrolling is worth more than one below it, which is the entire reason the leaderboard exists as a wide, shallow strip — it fits above a page’s content without pushing that content off the screen.
The margin formats work on the opposite principle. A skyscraper or half page sits alongside the article and stays visible while the reader scrolls, so it trades initial prominence for duration.
Mobile changes the arithmetic completely. There is no margin on a phone, so the formats that survive are the ones that fit the full width and take little height — which is why the mobile leaderboard looks nothing like its desktop namesake.
Questions people ask
Does a bigger ad perform better? Larger formats get more attention and cost more. The medium rectangle usually wins on availability rather than on impact.
Should I make a version for every size? Design two — one wide, one tall — and adapt. Redrawing each size from scratch is rarely worth it.
Do animated ads outperform static? Sometimes, and the final frame does most of the work either way.
Why was my ad rejected? Usually file weight, or text that overlaps the edge. Both are visible in a preview.
Build for the slot, then look at it in place. Banner ad sizes and Google display ad sizes list the current set, leaderboard and skyscraper cover the two named ones, Facebook ad size, carousel and Snapchat handle the social formats, and the ad mockup generator, ad preview tool, Google Ads preview and Facebook ad preview show the assembled result.