How to convert an audio file
- Click Drop an audio file here or click to browse and pick your file, or drag it onto the box. Use Try a 3 second sample tone if you only want to see how it works.
- Under Convert to, choose WAV or MP3. For MP3, set the MP3 bitrate that appears.
- Set the Sample rate (44,100 Hz for music and general use, 48,000 Hz for video projects) and Channels (Stereo or Mono).
- Press Convert, listen to the preview, then press Download converted audio.
How the conversion works
Your browser first decodes the file into raw samples with the Web Audio API (decodeAudioData) and resamples it to the rate you chose. Stereo to mono averages the left and right channels, and mono to stereo plays the same signal in both. Sources with more than two channels are mixed down by the browser.
WAV output is uncompressed 16-bit PCM, so its size follows a fixed formula: 44 header bytes plus seconds × sample rate × channels × 2. MP3 output is encoded at a constant bitrate with lamejs, a JavaScript port of the LAME encoder, so its size is about seconds × bitrate ÷ 8. The encoder library is downloaded only the first time you choose MP3.
WAV keeps everything the browser decoded. MP3 is always lossy, so converting a lossy file again loses a little more detail.
Worked example with the sample tone
The sample is a 3 second, 440 Hz tone saved as a mono WAV at 44,100 Hz, which is 258.4 KB. Convert it to WAV at 44,100 Hz and Stereo and the output is 44 + 3 × 44,100 × 2 × 2 = 529,244 bytes, shown as 516.8 KB. Convert it to MP3 at 192 kbps and the size drops to 71.0 KB, close to 3 × 192,000 ÷ 8 = 72,000 bytes, with the same 3 second duration.
Limits and edge cases
- Files up to 150 MB are accepted. Long recordings can still run out of memory on phones, because the whole file is decoded first.
- WAV is almost instant. MP3 encoding is slower, about 3 seconds per minute of audio on a laptop and longer on a phone.
- The outputs are WAV and MP3 only. FLAC, OGG and M4A are accepted as input but not produced.
- If a file will not open, the format or codec is not supported by your browser. Try Chrome, Edge or Firefox, or another copy of the file.
- Tags and cover art are not carried over, and there is no trimming or volume change.
- To make a new recording first, use the Audio Recorder or the Voice Memo Recorder. To compare file sizes, use the Data Storage Converter.
Frequently asked questions
Will converting MP3 to WAV improve the sound quality?
No. An MP3 has already lost detail, and a WAV made from it keeps that loss while being many times larger. Convert to WAV when an editor or device needs it, not to improve the sound.
Is my audio file uploaded to a server?
No. The file is read, decoded and encoded inside your browser. The only download is the MP3 encoder library from a public CDN the first time you choose MP3.
Which MP3 bitrate should I choose?
Use 128 kbps for speech and podcasts, 192 kbps for everyday listening and 256 or 320 kbps for music you care about. One minute is about 1 MB at 128 kbps and 2.4 MB at 320 kbps.
Should I choose mono or stereo?
Use stereo for music and mono for a single voice. Mono mixes both channels together, so nothing is lost if the voices were on separate channels. For WAV it halves the file size. For MP3 the size depends on the bitrate you pick.
Why can't this tool convert to FLAC, OGG or M4A?
Browsers can decode those formats but have no built-in encoder for them, and adding one means shipping a large codec. WAV and MP3 cover most needs, and FFmpeg or Audacity handle the rest.
Sources: MDN, decodeAudioData, the Web Audio API channel mixing rules and lamejs.