Length of Songs

Most contemporary popular music clocks in between three and five minutes of length, so most online estimators assume files of roughly that duration. However, you may have other things in your collection that can skew your estimations such as remixes or digitized 12-inch vinyl singles. These can be significantly longer than the usual song length—as can be orchestral works, operas, podcasts, and similar content.

Bitrate and Encoding Method

The bitrate used for encoding a song has a large effect on file size. For example, a song that is encoded at 256 Kbps yields a larger file size than the same song encoded at a bitrate of 128 Kbps. The encoding method can also affect how many songs will fit on your portable device—variable bitrate files generate a smaller file compared to constant bitrate files. One reason the VBR vs. CBR question matters is that VBR files generally produce better sound and sometimes result in smaller files if the audio properties of the original sound support it, but they decode more slowly and thus some playback devices cannot handle them. CBR is universally accepted despite known limitations in acoustic quality.

Audio Format

Choosing an audio format for your particular portable is also an important factor to consider. The MP3 standard may be the most widely supported audio format, but your device may be able to use an alternative format that produces smaller files. AAC, for example, is regarded as being better than MP3. It typically produces higher quality audio and is more efficient at compression. This format could give you more songs per gigabyte than if you use MP3 alone. Other formats, like Windows Media Audio, Ogg Vorbis, and the Free Lossless Audio Codec, can yield smaller file sizes with richer acoustic properties than MP3, but MP3 as a standard—except for Apple, which relies on AAC—means you can always play an MP3 but perhaps not any of the other types, depending on the hardware you’re using.

Figuring It Out

Assuming you’ve opted for the more universal MP3 format for your music library, there’s a really simple formula that you can use to estimate how many songs will fit in 1 gigabyte. This isn’t an exact science, but it’ll give you a good idea. Take the length of the song in seconds. Then, multiply it by the bitrate of file. 128 Kbps is the standard for MP3s, but you can also find plenty in 256 Kbps and 320 Kbps. Now, take the result, and divide it by the result of 8 multiplied by 1024. That will convert from kilobits(kb) to megabytes(MB). All together, it looks like this: (seconds * bitrate) / (8 * 1024)
That will give you an approximate size for a single song, but what about a whole library. Well, you could sit and individually calculate all of your songs, but who’d actually want to do that? Instead, take an estimate. Assume that the average length of your songs is 3.5 minutes. That’s pretty standard. Now, apply the formula. Remember to multiply 3.5 by 60 to get the number of seconds. ((3.5 * 60) * 128) / (8 * 1024) The result is a rough estimate of 3.28 megabytes(MB) per song. Does that seem about right for your library? To figure out how many 3.28MB songs can fit in a gigabyte(GB), divide 1024 by 3.28 because there are 1024 megabytes in one gigabyte. 1024 / 3.28 There you have it! You can fit roughly 312 songs on 1GB of storage. If you really don’t feel like doing all the math, you can remember that, for MP3s at a bitrate of 128 Kbps, 1 minute of audio equals about 1MB.

Examples

Assume a smartphone with 4 GB of available data storage. If your pop-music library averages 3.5 minutes per song, at 128 Kbps each in the MP3 format, then you’ll have a bit over 70 hours of music available, good for nearly 1,250 songs. With the same amount of space, your collection of symphonies clocking in at 7 minutes per track at 256 Kbps yields a bit more than 36 hours of music, a total of 315 songs. Conversely, a podcast pushing out monaural sound at 64 Kbps and running for 45 minutes per episode gives you 140 hours of talking over 190 shows.

Alternatives to File Transfers

It’s less common to download audio files to portable devices, as it was when devices like the iPod or the Zune led the market, as streaming services like Spotify and Pandora become more common on smartphones. If you’re running into a space crunch, consider ditching the file library and matching your MP3s with a streaming service. You’ll get the benefit of your music without losing space on your smartphone—plus, you can often download specific playlists to get you through those times when you don’t have cell or Wi-Fi signals.

Other Considerations

The MP3 format supports tags and album art. Although these assets aren’t generally large, they do add a bit of extra padding to individual file sizes. Particularly with podcasts and other spoken-word tracks, a file collapsed from stereo to mono takes up less space, often with little effect on the listening experience. Although it’s up to audio producers to select the right audio format and bitrate for their music, if you need to shave off some megabytes off your MP3 collection, take advantage of software that dynamically re-sizes MP3s or other audio files.