What Is a Normal MP3 Bit Rate?

A normal MP3's bit rate falls between 128 kilobits per second, or kbps, and 320 kbps. Different bit rates in this range have different advantages; when you're ripping music from a CD to MP3, choose the bit rate that's best suited for your purposes. In general, the higher an MP3's bit rate, the better its audio quality, but the larger its size. The most common MP3 bit rates are 128 kbps, 192 kbps and 320 kbps.

Bit Rate

The bit rate of an MP3 indicates the density of the audio information contained in the file. Every second in a 192 kbps MP3, then, contains 192 kilobits -- 24 bytes -- of data. The higher the bit rate, the more information the MP3 contains; the more information it contains, the closer it is to the original audio recording. The bit rate also determines the MP3's file size: a four-minute song encoded at 128 kbps takes up just over 3.5 MB, while the same song encoded at 320 kbps requires over 9 MB of space.

Choosing a Bit Rate

When you're converting a sound file or ripping your CD collection to MP3, you must specify the bit rate that you want the encoder to use. Choose a bit rate based on the type of audio that you're encoding and its desired purpose. If you're converting a lecture or other spoken-word piece of audio, a bit rate of 128 kbps is more than sufficient. If you're encoding MP3s for use with a portable media player, a bit rate of 192 kbps usually provides a good balance between audio quality and file size. If you're archiving your CD collection to the MP3 format, encode the files at 320 kbps.

Variable Bit Rate

Variable bit rate encoding changes an MP3's bit rate depending on the type of data present at a given point in the audio. For example, a variable bit rate encoder might encode an information-dense portion of an MP3 at 320 kbps; when the audio contains a section of silence, however, the encoder drops the bit rate down to 32 kbps. If an MP3's bit rate is an unusual number -- 204 kbps, for example -- this indicates that the MP3's creator encoded it with a variable bit rate.

Converting Bit Rates

Although most MP3 conversion and encoding programs can change an MP3 to a different bit rate, this is not, generally speaking, a good idea. Converting an MP3 to a higher bit rate does not add any more audio information to the file, so the sound quality does not increase. Converting an MP3 to a lower bit rate reduces its file size, but may also introduce audio artifacts, as the encoder is compressing an already compressed file. If you need an MP3 file to be in a different bit rate, re-encode an MP3 from the source CD audio or WAV file.