The Universal Mobile Banner
The 320x50 mobile banner is the foundational ad unit of mobile advertising. Originally designed to match the 320-pixel viewport width of early smartphones, it has become the universal standard for mobile banner ads across both mobile web and in-app environments. Every major mobile ad network, SDK, and mediation platform supports this size. It is the default banner format in Google AdMob, Facebook Audience Network, Unity Ads, and virtually every other mobile monetization solution. Despite the emergence of newer adaptive banner formats, the fixed 320x50 unit remains the most widely served mobile ad format globally.
Placement Strategies for Mobile
The 320x50 banner is most commonly anchored to the bottom of the screen in mobile apps, where it remains persistently visible as users interact with the content above it. On mobile web, it typically appears at the top of the page below the header or between content sections. Avoid placing the banner too close to navigation elements or interactive content to prevent accidental clicks, which can lead to ad network policy violations and poor user experience. The Coalition for Better Ads recommends against sticky mobile ads that cover more than 30% of the screen, but the slim 50-pixel height of this banner keeps it well within acceptable limits.
Adaptive Banners vs. Fixed 320x50
Modern mobile screens range from 360px to over 430px in logical width, which means a fixed 320x50 banner leaves unused space on most current devices. Google introduced adaptive banners that automatically adjust their width to fill the available screen width while maintaining an optimal height. Adaptive banners can serve sizes like 360x50, 390x50, or 414x56 depending on the device. However, many ad networks still require the classic 320x50 creative as a fallback. When designing mobile ad creatives, produce both a 320x50 fixed version and test with adaptive banner implementations to maximize fill rate and visual appearance across the device landscape.
Design Constraints and Optimization
Designing within 50 pixels of height is extremely restrictive. Effective 320x50 banners distill the message to its absolute essence: a short headline of three to five words, a brand mark or small logo, and an action word or CTA. Avoid any text smaller than 10px as it will be illegible on mobile screens. Use solid background colors rather than gradients or complex imagery, which become muddy at this scale. File size should stay under 150KB, and animations should be subtle since the small area cannot support complex motion without looking chaotic. Always verify that the banner is legible on both light and dark mode interfaces, as many apps and mobile browsers now support dark themes that may affect how your ad border is perceived.