What Is a Mobile Interstitial Ad?
The 320x480 mobile interstitial is a full-screen ad format that covers the entire viewport of a mobile device. Unlike banner ads that coexist with content, interstitials take over the screen at natural transition points, such as between game levels, after completing an action, or when navigating between pages. The 320x480 dimensions correspond to the portrait orientation of classic smartphone screens and remain the standard static creative size for interstitial ads across most ad networks. Modern implementations often use adaptive interstitials that scale the creative to fill the actual device screen, but 320x480 serves as the baseline canvas size that gets scaled up.
Compliance with Better Ads Standards
Interstitial ads are subject to strict industry regulations due to their intrusive nature. Google penalizes mobile web pages that show interstitials immediately on page load, particularly when they block content that users arrived to see from a search result. The Coalition for Better Ads has established that interstitials must include a clearly visible close button, should not appear before the user has interacted with the page, and must not be shown more than once per session on the same page. For in-app interstitials, Google AdMob requires a minimum interval of 60 seconds between interstitial displays. Always implement frequency capping to prevent user fatigue and high app uninstall rates.
Timing and Trigger Best Practices
The key to effective interstitial monetization is showing the ad at the right moment. The best trigger points are natural content breaks where the user expects a pause: between levels in a game, after submitting a form, when switching sections in an app, or upon returning to the app after a background period. Never show interstitials immediately upon app launch, during active gameplay, or in the middle of a task the user is performing. For mobile web, display the interstitial after the user has viewed at least two pages and only between page navigations, not during content consumption. These practices maintain a positive user experience while maximizing ad revenue.
Creative Design for Full-Screen Impact
The full-screen format gives you a large canvas, so take advantage of it with bold imagery and clear messaging. Design the creative at 320x480 for standard definition and provide a 640x960 or higher resolution version for retina displays. Place the primary message and CTA in the center of the screen, avoiding the top 50 pixels where the status bar may overlap and the bottom 60 pixels where the close button typically appears. Use a solid or simple gradient background that loads quickly, and keep the total file size under 200KB for static creatives. For HTML5 interstitials, ensure the initial load is under 200KB with a maximum total of 2MB. Include a visible close button in the top-right corner that appears within 5 seconds, as required by most ad network policies.