320×480 – Mobile Interstitial
The 320×480 ad unit is a mobile ad with dimensions of 320 pixels wide by 480 pixels tall. This ad size is known as a Mobile Interstitial. It is generally pretty effective but also pretty annoying.
This ad size is intended to be a full-screen ad on smartphones. 320x480s can also be used as a mobile video ad size and as the expanded size of a 320×50 ad.
Fun Fact
320×480 was adopted as the mobile interstitial as it was the screen size of iPhone 1, 3G, and 3Gs.
What it looks like
The mobile interstitial dimensions are 320 x 480 pixels. Below is an example of this ad unit.
Note that the close button is not on the ad itself but on the background.
As is typical of mobile interstitials, while the ad size is not full screen, the background is blacked out, making it effectively full screen.
Technical Information
The ad size should have been updated as screen sizes grew. However, it persists. This is primarily because 320×480 is still the default setting in many places (such as Google Ad Exchange) when people are trying to build mobile interstitial ads.
To make this work, most ad platforms black out the screen behind the ad unit, keeping it as a full-screen ad unit regardless of the screen size.
This ad size is also named incorrectly. It is called a Mobile Interstitial. However, Interstitial technically means an ad that appears between two pages. This means this ad loads when you click a link instead of loading the next page.
In online advertising, interstitial is generally used interchangeably with overlay (or floater) to mean an ad that loads on top of the content (but within the same browser window). Most of the time, you will see this ad as an overlay instead of a true interstitial.
320×480 Advice for Site Owners
If you get a lot of visitors to your site via mobile, you should consider running this ad size.
However, as with all overlay ads, you should limit the number of times any user sees this type of ad. This is because they are quite annoying to your visitors. The more often a user has their visit interrupted by an ad type like this:
- The more likely they are to leave
- The less likely they will return to your site.
This goal is always to build a large and loyal user base, so annoying them is a mistake. This ad type should be used sparsely, if at all.
If you have a small-to-medium site, I would recommend avoiding them. Growth should be your goal.
If you have a large established site, you could consider using them occasionally (once per hour per user). They can earn good RPMs – for mobile (which are generally much lower than desktop). However, keep in mind that scarcity drives up prices. So running more of these ads will only get you more money in the short term. Once you run them all the time for a while, their price will drop steeply, and you’ll have to start running a new, more annoying ad type.
Top Tip
If you are using AdSense, a frequency cap will be automatically applied. For other ad networks, you should probably consider a 1/1 frequency cap so an ad will appear for each user at most once per hour.
320×480 Advice for Ad Buyers
320×480 is a good ad size if you can find a site that serves it. This is because they are larger than the most successful ad unit – the 300×250. The general rule of thumb is the larger the ad size, the better the performance.
They are also better designed to fit a mobile screen and, as an overlay, will generally perform well. Make sure to include an easy-to-use close button, as accidental clicks from badly designed ads aren’t really worth anything to advertisers. People will click away, but those clicks may still cost you money and give the algorithm bad signals about who is interested in your ad.
Also, as noted above, some ad platforms will build a close button on the background (which they will black out while your ad serves). Check before building your ad.
Summary
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