This article explains how to set a song as a custom iPhone ringtone using iTunes 9, 10, 11, and 12.

The process starts on your computer, where you use iTunes to select a 30-second snippet of a song and export the clip of that song in a file format your iPhone can recognize as a ringtone.

Launch iTunes on your computer. It’s always a good idea to make sure you’re running the latest version of iTunes, especially if you don’t use it often, to ensure it syncs properly with your phone. If iTunes offers to install the latest update, wait for that to happen before proceeding.

In your iTunes music library, find a song you want to use as a ringtone and click on it to select it.