Mobile Banner Ad Sizes 2026: 320×50, 320×100, 300×250 and 320×480 (Drawn at Actual Size)

Mobile banners are where most display impressions happen and where most banners look worst. The sizes are tiny, the screens are dense, and a design that was approved as a 300×250 on a desktop monitor turns into an unreadable strip at 320×50.

This guide covers the mobile sizes that still get bought in 2026, drawn at actual pixel size so you can judge them the way a phone shows them, plus the design rules that keep text readable and the set to build when the brief just says "mobile".

The short answer: build these four

Size	Name	Where it runs
320×50	Mobile Leaderboard	Top or bottom of the screen, often sticky. The most common mobile strip.
320×100	Large Mobile Banner	Same slots, twice the height. Usually the better performer of the two.
300×250	Medium Rectangle	In-feed and in-article on mobile, same file as desktop.
320×480	Mobile Interstitial	Full screen, between actions in apps and games. Only if the media plan includes interstitials.

Add 300×50 only if a publisher asks for it; it is a narrower 320×50 that a few older ad slots still use.

320×50Mobile Leaderboard

320×100Large Mobile

300×50Mobile Banner

Each size, at actual size

320×50 — Mobile Leaderboard

The size everybody buys and nobody enjoys designing. Fifty pixels is about the height of one line of large text plus a little air. What fits: a logo on one side, four or five words, and a button shape on the other side. What does not fit: a product shot, a price and a disclaimer at the same time.

320 × 50Mobile Leaderboard

Because it often sits sticky at the bottom of the screen, it is also the size with the most accidental taps. Keep the call to action clear and the layout calm; a 320×50 that flashes or crams in three frames of copy gets ignored or tapped by mistake, and neither helps the campaign.

320×100 — Large Mobile Banner

Same width, double the height, and a lot more room to work with: two lines of copy, a small product image, a real button. If the brief allows only one mobile strip, this is the one to argue for.

320 × 100Large Mobile Banner

300×50 — Mobile Banner

Twenty pixels narrower than 320×50 and otherwise identical. It exists because some older placements were built for it. Make it only when a publisher's spec sheet lists it, and adapt it from the 320×50 rather than designing it separately.

300 × 50Mobile Banner

300×250 — Medium Rectangle

The desktop workhorse is also the most common mobile in-content size. The same file serves both, which is convenient and also a trap: check it on a phone, at the size a phone shows it, before the client approves it on a 27-inch monitor.

300 × 250Medium Rectangle

320×480 — Mobile Interstitial (portrait)

A full-screen ad shown between actions: between levels in a game, between articles in an app. It is the only mobile size with room for a proper layout, an image, a headline and a clear button. The platform adds its own close button, usually in a top corner, so keep that corner free of anything important. There is a landscape version, 480×320, for apps that run sideways.

320 × 480Mobile Interstitial (portrait)

Design rules for small sizes

• Design the 320×50 first. If the message fits in fifty pixels, every other size is an adaptation. If you start from the 300×250, you will reach the 320×50 last and find the headline does not fit.
• One message per frame. A mobile strip is seen for a second or two while someone scrolls. Three rotating frames of copy means most people see one of them, at random.
• Text size: think in phone pixels. Copy that is 11 px in a 320×50 is 11 px on the phone too. Anything under about 12 px is decoration, not reading material.
• Export images at 2×. Phones have dense screens, so a 320×50 drawn with 320×50 assets looks soft. Use images at twice the size (640×100) inside the banner and keep the banner itself at 320×50. Watch the weight while you do it.
• Keep the edges calm. The strip sits next to the phone's own interface or the page's content. A thin border or a solid background colour stops it from bleeding into the page.
• Check animation on a real phone. CSS animation that is smooth on a desktop can stutter on a mid-range phone, especially with large images moving.

Weight and format

Mobile sizes follow the same limits as the rest of the set: the platform maximums are generous, but the brief is usually stricter. 150 KB per banner is still the most common line in a media plan, and IAB's lean guidelines put the initial load at 200 KB. The full numbers per platform are in our HTML5 banner specs 2026.

Two things matter more on mobile than on desktop:

• Initial load. On a phone connection, a banner that loads 400 KB before it shows anything is a blank rectangle for the first seconds of the impression.
• Backup images. Some mobile placements still serve the static backup instead of the HTML5. Make sure the backup works on its own, with the logo and the message, not just the first frame of the animation.

Which mobile set to build

• Google Display Network, mixed devices: 320×100 and 300×250 on top of the desktop set. Add 320×50 if the plan says "all sizes".
• Mobile-first performance campaign: 320×50, 320×100, 300×250.
• App campaign or gaming network: the above plus 320×480 (and 480×320 if the app runs in landscape).
• Direct buy with a publisher: ask for their spec sheet first. Publishers often add their own mobile sizes, such as a 300×600 mobile half page or a 320×480 in-article unit, with their own weight limits.

Show the client the mobile sizes at mobile size

The most common review mistake with mobile banners is approving them blown up. A 320×50 opened as an image on a desktop is shown at whatever zoom the viewer picks, and the client judges the typography on that.

On a BannerPeek preview page every size runs at its real pixel size, next to the rest of the campaign, and the client can open the same link on their phone to see the mobile sizes the way the audience will. Comments go on the banner itself, approvals carry a name and a time, and the next round goes on the same link.

Quick reference

• 320×50 — the mobile strip everyone buys; design it first
• 320×100 — the better strip, if the brief allows it
• 300×250 — in-feed on mobile, same file as desktop
• 320×480 — full-screen interstitial, apps and games
• 300×50 — only when a publisher asks for it

Related reading

• Banner ad sizes 2026: every desktop and mobile size, drawn at actual size.
• HTML5 banner specs 2026: weight limits and requirements per platform.
• How to share banner ads with clients: getting the whole set reviewed without zips.