Will an iPhone app run on an iPad? And will an iPad app run on an iPhone? Allow us to explain the difference between iPhone-only, iPad-only and universal apps, and how you can run iPhone-only apps and games on an iPad (and vice versa).

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Will my app run on iPad, iPad mini, iPhone and iPod touch?

Not all iOS apps run on all iOS devices. We knew that, right? The most obvious obstacle relates to how up-to-date your hardware and software are, but it also relates to the type of hardware you've got.

If you're looking at an app on the App Store, look at the Compatibility section - it's under the first Details tab, then under Information.

Which Apple devices is an app compatible with?

As an example, above is a new iOS game called Icycle: On Thin Ice. Under Compatibility (at the bottom) you can see it’s compatible with iOS 6.1 or later (see How to update your iPhone or iPad to iOS 7), and with the iPhone 4 and later, iPad and iPod touch. This is what we call a universal app: one that runs on iPhone, iPod touch, iPad and iPad mini.

Will an app for iPad also run on iPad mini?

Yes - if it'll run on iPad, it’ll also run on iPad mini (and iPad mini 2). That's supposed to be implied, but can be confusing.

The four types of iOS apps, and the devices they run on

So we’ve got four types of iOS app:

1. Universal apps and games: increasingly common. Hopefully one day all apps will be universal. It runs on all four types of iOS device (although it'll look slightly different on each, thanks to the varying screen ratios), and if you buy the app for one you'll be able to download it on another format for free.

2. Multiple-version apps and games: In this case the developers have created two versions of the app. One is for iPad and iPad mini, and the other is for iPhone and iPod touch. You’ll be able to tell because the two versions will have slightly different names (the iPad version is likely to have 'HD' or 'for iPad' tagged on the name) and and probably different prices.

An example of this kind of app is Kingdom Rush. If we search for 'kingdom rush' on the App Store we clearly see two different versions of both Kingdom Rush and Kingdom Rush Frontiers, with the iPad versions labelled as 'HD' and with price tags that are a pound higher.

Which Apple devices are apps compatible with?

If we click on one of the 'standard' games, you'll see, confusingly, that the iPad is included in the Compatibility section - that's because even 'iPhone-only' games can be run on an iPad, as we'll see later. But you won’t be getting the improved graphics the developers will have added to the iPad version.

Is this app compatible with iPhone and iPad?

If we click on the HD version we see that the Compatibility field only has the iPad (and, by implication, the iPad mini).

Is this app compatible with iPhone and iPad?

3. iPhone-only apps and games: Increasingly rare. This is an app that was designed for iPhone and never got adapted for the iPad screen. Sometimes this will be the case because the developers simply haven’t got around to making an iPad version. Other times they just prefer the iPhone experience.

Here's an example: the venerable free RPG Undercroft (a nice little Eye Of The Beholder-esque retro number). It was last updated at the start of 2011 so it's little surprise that they haven't got round to doing an iPad version.

A search for 'undercroft' on iTunes reveals only an iPhone app: searching on our iPad brings up no results at all. To see apps and games that aren't designed for iPad, click 'iPad Only' at the top and select iPhone Only.

How to see iPhone only apps on an iPad

We can still run Undercroft on the iPad, however, as we’ll see later.

4. iPad-only apps and games: This is a more serious restriction, and if an app is designed only for iPad, you won’t be able to play it on iPhone - not without jailbreaking, anyway. We talk about that at the end of the article.

An example of this is Fingle - a somewhat suggestive party game where you and a partner have to put your fingers on moving spots on the screen. It's understandable that this wouldn't work on iPhone.

Does this app run on iPad and iPhone?

How to run an iPhone app on an iPad

Let’s get Undercroft running on the iPad. Simply tap the app icon to start the game, and you’ll see that it appears to be running normally - except for a circle at the bottom right with 1X. If you click this the game will run at its normal resolution in an iPhone-sized window. By default the game runs at double resolution.

So your options (neither of which is ideal) are to run it at twice its native resolution, which will make it look grainier than it would on an iPhone:

How to run an iPhone app on an iPad

Or use only part of your screen:

How to run an iPhone app on an iPad

Will iPad-only apps run on an iPhone? How to run iPad apps on iPhone

Want to know how to make iPad-only apps and games work on an iPhone? It isn't easy, but if you've got a jailbroken iPhone it can sometimes be done. (How well the app runs on the iPhone - or if it runs at all - depends on the way the app is designed.)

If you want to know how to jailbreak your iPhone, take a look at our iPhone jailbreaking instructions.

You’ll need to have access to the app's .ipa file, and a Mac app called iTelePad2Pod. idownloadblog has the instructions. Just remember that jailbreaking your iPhone is likely to invalidate your warranty.

David Price on Twitter | Macworld on Twitter

See also:

How to block a phone number on any iPhone, in iOS 7 and iOS 6

How to downgrade an Apple device from iOS 7 to iOS 6