As of March 2011, the iPhone 4 is available with a choice between 16GB and 32GB of storage space, which means you can take music, videos and other types of media with you anywhere. Your iPhone stores your contacts, call history and text messages, but these types of files do not use much of your iPhone's memory. Audio files, video files and large apps can account for large portions of your memory usage on the iPhone.
Evaluating Your Memory
When you plug your iPhone into your computer to sync through iTunes, your iPhone provides a visual display of current memory usage. Click the device icon for your iPhone, located in the left column of the iTunes application window. This takes you to the summary window, which has a gray "Capacity" bar to show you how you're using memory on your iPhone. The capacity bar lists audio usage, video usage, app usage, photo usage and remaining free space. Audio podcasts are listed with audio files and video podcasts are listed with video files.
MP3 audio file size can vary based on sound quality. For MP3s with a bit rate of 128kbps, you can estimate that one minute equals one megabyte; so a four minute song would be about four megabytes of information. Songs purchased from the iTunes Store have a higher audio quality of 256kbps, which increases the file size. A four minute song with a bit rate of 256kbps is approximately 7.5 megabytes. This means that a 16GB iPhone can hold approximately 5,300 3-megabyte songs or 2,200 7-megabyte songs.
If you purchase TV shows and movies for your iPhone from Apple's iTunes Store, these high-quality video files can use up a lot of memory on your iPhone. The iTunes Store offers both regular and HD video, both of which can have large file sizes. For example, the average two-hour movie from the iTunes Store is approximately 1.3GB and the HD version of the same movie is approximately 2.93GB. The iPhone's 5-megapixel cameras record HD video at up to 30 frames-per-second, but the size of your videos will depend on recording length.
Apps and Other Files
The functions and size of an app will determine how much memory it uses on your iPhone. iPhone apps can range from small, such as the Facebook for iPhone app, which is 7 megabytes, medium sized, such as Skype, which is 20 megabytes, or very large, such as the Magellan Road Mate, with is 1.34GB. You can also use third-party applications to store files and folder on your iPhone, in which case the space files take up on your iPhone depends entirely on the size of the file.