WMA Vs. MP3 File Size


Windows Media Audio (WMA) files were developed by Microsoft in the late '90s as a more-efficient competitor to the popular MP3. While some of Microsoft's claims about the relative sound quality of the two formats have been disputed, WMA files do often have lower bit rates than MP3s. However, a MP3 and a WMA encoded at the same bit rate would be the same size.

About MP3

  • MP3s are compressed audio files. They contain nearly all the information of the original CD, but obtain a smaller file size by dropping the highest and lowest tones. The smaller the MP3's bit rate, the greater the compression, and the more data lost. Generally an MP3 only throws away sounds the human ear cannot hear, but MP3s compressed too heavily will sound thin and tinny.

About WMA

  • Microsoft developed Windows Media Audio (WMA) in 1999 as a competitor to the popular MP3, claiming that the sound quality of a WMA file encoded at 64 kbits/s equaled or exceeded that of an MP3 encoded at 128 kbits/s. Unlike the MP3, WMA files cannot be played in iTunes or on iPods, and have not proven to be the death of the MP3 as Microsoft hoped.


  • Microsoft has garnered criticism for its claims about the quality of WMA files. While a 1999 test by National Software Testing Laboratories (funded by Microsoft) claimed that 64 kbits/s WMA were preferable to 128 kbits/s MP3, several studies since have disputed these claims. In 2003, audio tester Roberto Amorim reported that listeners preferred MP3 with 99 percent confidence, writing that "No codec delivers the marketing plot of same quality as MP3 at half the bitrates."

Standardizing Bit Rates

  • To compare the relative sizes of song encoded in WMA and MP3 formats, the encoding bit rate must be standardized. An MP3 encoded at 320 kbits/s would certainly be a larger file than a WMA encoded at 64 kbits/s and vice versa. The two files need to be examined at comparable bit rates.

File Size Comparison

  • By definition, an MP3 and a WMA file encoded at the same bit rate will be the same size. For instance, a 1 second file encoded at 128kbit/s will take up 128kbit of space, regardless of conversion codec. However, in practice, WMA files are often smaller than MP3, since many believe a WMA of a smaller bit rate sounds just as good as an MP3 at a larger one.

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  • Photo Credit "Discovering Vampire Weekend (4th/52)" is Copyrighted by Flickr user: skippyjon (Alexandre Normand) under the Creative Commons Attribution license.
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