iPhone 4 and iPhone 4S are so popular now. But it comes with a small selection of default ringtones and it’s really not worth paying Apple $1 for a songs and then paying $1 extra to "make" it to a 40 sec iPhone 4 ringtone. That’s why so many people are looking for ways to make ringtones for iPhone 4 on Mac, including you.
There are actually many ways to create iPhone 4 ringtones on Mac. In this article, two ways are introduced: one is using an iPhone ringtone maker for Mac and the other is using iTunes to generate free ringtones for iPhone 4.
The easiest way to make iPhone ringtones on Mac is to get an iPhone ringtone maker for Mac and let it do the rest for you. Here Video Converter for Mac is strongly recommended to make iPhone 4 ringtones on Mac. With it, you can not only generate iPhone 4 ringtone from audio files, but also extract ringtones for iPhone 4 from video files. Now download it and follow the guide below. If you are using Windows, please turn to Video Converter Ultimate.
The main interface of this Mac Video Converter is as below, you can complete making iPhone 4 ringtones on Mac with it in the following three simple steps.

You can add audio files in AAC, MP3, M4A, WMA, WAV, AIFF, AC3, OGG, APE, etc. formats and video files in MP4, WMV, ASF, MPG, 3GP, FLV, AVI, MOV, VOB, H.264, M2TS, TP, TS, etc.
Select the clip and click "Edit" to trim so as to get the very part you want. Remember the audio length shouldn't exceed 40 seconds. Real-time preview is available so that you can make sure the part you choose is exactly what you want.
Select M4R as the output audio format and start generating iPhone 4 ringtones on Mac.
You can also make free iPhone 4 ringtones with iTunes. This may be a little complicated, but it works. The detailed guide is as below:
Open your iTunes and go to "Preference" in the iTunes menu at the top. Then choose the "General" tab and select "Import" settings. Then in the "Import Settings" window, choose "AAC Encoder" as the import encoder and make sure the bit rate is 128kbps.

After that, go back to iTunes library and find the song you want to make into a ringtone. Listen to the song and find the part of it you want to use and remember the start and end time. Then right click the same of the song and select "Get Info". A window like below will pop up. Go to "Options" and set the the 'Start Time' and 'Stop Time' to the appropriate interval that you like the best - remember that the length can only be a maximum of 40 seconds. When you're done, click "OK" to save the settings.

Next, in the iTunes menu at the top, click "Advanced", then Create AAC Version from the drop-down menu. iTunes will then create a duplicate version of the song you've selected.

After that, you can right click on that track and select "Show in Finder". Then copy the song and save it in the same folder so that a third version appears. Afterwards, you can rename the track on the desktop from "track name.m4a" to "track name.m4r".

The last step is to delete the duplicated track from your iTunes library by right clicking the track and choose "Delete". And double-click on the new .m4r file and it will be added into iTunes as a ringtone which can be synced to your iPhone 4/iPhone 4S.