If you are looking to monetize a mobile app or a mobile-optimized website, there is one ad size that consistently delivers the highest revenue: the 320×480 Mobile Interstitial.
Unlike small banners that sit politely at the bottom of the screen, the 320×480 format is bold. It was originally designed to fill the entire screen of early smartphones (like the original iPhone). Today, on modern, taller screens, it acts as a massive “modal” or “overlay” that commands 100% of the user’s attention.
In this guide, we will explore why this format commands such high CPMs (Cost Per Mille), where to place it without annoying your users, and how to design it for maximum conversions.
What is the 320×480 Interstitial?
The 320×480 ad unit is a vertical rectangle that measures:
- Width: 320 pixels
- Height: 480 pixels
- Aspect Ratio: 2:3
It is commonly referred to as a “Mobile Interstitial” because it usually appears at natural transition points—like between levels in a game, while a page is loading, or before a video starts. Because it covers the content, the user must either interact with the ad (click) or close it to continue.
Why Advertisers Pay More for This Size
Advertisers love this format, and they are willing to pay top dollar for it. Here is why:
1. 100% Viewability
You can’t miss it. Unlike a small 320×50 banner that users might scroll past, the 320×480 forces the user to look at the creative. This guarantees visibility, which is a key metric for big brands.
2. “Canvas” for Creativity
With 480 pixels of vertical space, designers have room to tell a story. They can include a high-quality product image, a headline, a bulleted list of benefits, and a large “Shop Now” button. This leads to higher engagement and more clicks.
3. High Click-Through Rates (CTR)
Interstitials typically see CTRs that are 5x to 10x higher than standard banner ads. While a banner might get a 0.5% CTR, a well-designed 320×480 can easily hit 3% to 5%.
Best Practices for User Experience
The danger of the 320×480 format is that it can be intrusive. If you use it wrong, you will annoy your users and drive them away. Follow these rules to keep your audience happy:
- Use Frequency Capping: Never show an interstitial every time a user clicks. Limit it to once per session or once every 5 minutes.
- Natural Breaks Only: Only show these ads during a “break” in the action—like after a user finishes reading an article or completes a game level. Never interrupt a user while they are reading or playing.
- Clear Close Button: Ensure the “X” or “Close” button is clearly visible. Hiding the close button is a violation of Google policies and frustrates users.
Conclusion
The 320×480 Mobile Interstitial is a high-risk, high-reward format. When used sparingly and strategically, it can significantly boost your ad revenue and provide advertisers with the engagement they crave. It turns a passive mobile browsing experience into an interactive one.