How to convert M4A to MP3: drop the file, pick a bitrate
This M4A to MP3 converter decodes the audio inside an M4A file and compresses it again as MP3. Drop your files in the box above, pick a quality (the bitrate), and press "Convert to MP3." A good starting point is 192 kbps for music and mono 64 kbps for voice recordings. A bitrate higher than the original does not make the sound better. It makes the file bigger without making it sound better than the source.
For example, the tool's sample file (a 20-second song, about 242 kbps AAC, 612 KB) comes out at 485 KB at 192 kbps and at 807 KB at 320 kbps, which is larger than the original. Nothing is uploaded: the conversion happens inside this browser.
When you need an MP3 instead of an M4A
Most phones and computers play M4A without trouble, but an MP3 is still the safer choice in a few situations.
- Older car stereos and MP3 players: many head units and portable players read music from a USB stick or SD card only if it is MP3.
- Voice memos from an iPhone: exporting a voice memo to the Files app gives you an .m4a file. If the person you send it to uses a program or device that will not open M4A, MP3 is the safest format.
- Upload forms, older editing software and shared drives: some forms and audio tools list MP3 as the accepted sound format. Check what yours accepts before you convert.
- Smaller files: a recording saved as lossless ALAC can take several MB per minute. At MP3 128 kbps a minute takes about 0.96 MB.
If the place you are sending the file to already accepts M4A, leave it alone. AAC and MP3 are both lossy, so a second conversion can only remove a bit more detail. Apple's Music help says the same: converting between compressed formats may reduce sound quality.
How to use it
- Drag M4A files into the box or press "Choose M4A files." You can add up to 20 files at a time, each up to 100 MB. The list shows each file's codec, bitrate, length and tags as soon as it loads.
- Pick a bitrate on the quality ladder. Every step shows the estimated MP3 size and the highest frequency it keeps, and the red dashed line marks the size of the original.
- If you like, choose the channels (keep the original or mono) and turn "Keep tags and cover art" on or off. The Voice preset is mono 64 kbps, Music is 192 kbps and Best is 320 kbps.
- Press "Convert to MP3." The first time, the converter engine (about 32 MB) downloads once. Each file draws its waveform from left to right as it converts.
- Press play to listen. The Original | MP3 switch under "Listen" changes the sound at the same position in the track. Save files one by one, or use "Download all" to get a single ZIP.
M4A, AAC, ALAC and MP3: what is the difference?
M4A is the file extension for an MPEG-4 file that holds only audio. The sound inside is usually AAC (lossy) or ALAC (lossless). The extension alone does not tell you which, so the tool reads the file's structure as soon as you add it and shows the codec and bitrate.
| Format | What it is | Compression | In this tool |
|---|---|---|---|
| M4A | Extension for an audio-only MPEG-4 file | Depends on the codec inside | Read. Audiobooks (M4B) and ringtones (M4R) use the same container and are read too |
| AAC | The codec most M4A files use | Lossy | Read. The source bitrate is shown |
| HE-AAC | An AAC extension tuned for low bitrates | Lossy | Read. The real sample rate is shown even when the file lists half of it |
| ALAC | Apple's lossless codec | Lossless | Read. Converting to MP3 makes a lossy copy |
| MP3 | MPEG-1 and MPEG-2 Audio Layer III | Lossy | The output (constant bitrate, CBR) |
MP3 has been around for a long time, so it plays on very old hardware too. The MP3 licensing program run by Technicolor and Fraunhofer IIS ended on April 23, 2017.
Choosing a bitrate: file size and the frequencies kept
The tool saves MP3 at a constant bitrate (CBR), so the size depends only on the length: bitrate (kbps) × seconds ÷ 8 = KB. A three-minute song at 192 kbps is 192 × 180 ÷ 8 = 4,320 KB, or about 4.3 MB. The number of channels does not change the size. At 64 kbps, mono and stereo files are the same size, and mono simply spends all of those bits on one channel.
"Top frequency kept" is the low-pass frequency that LAME, the MP3 encoder this tool uses, sets for each bitrate. Anything above it is discarded so the remaining bits can go to the lower range. Humans hear up to about 20,000 Hz (20 kHz), so at steps that cut off near 11 kHz, such as 64 kbps stereo, the very top end, like the shimmer of a cymbal, is what disappears.
| Bitrate | 1 minute | 1 hour | Top frequency (stereo) | Mono | Good for |
|---|---|---|---|---|---|
| 64 kbps | 0.48 MB | 28.8 MB | 11.0 kHz | 16.5 kHz | Speech recordings (mono) |
| 96 kbps | 0.72 MB | 43.2 MB | 15.1 kHz | 20.5 kHz | Lectures and meetings |
| 128 kbps | 0.96 MB | 57.6 MB | 17.0 kHz | 20.5 kHz | Music when size matters most |
| 192 kbps | 1.44 MB | 86.4 MB | 18.6 kHz | 20.5 kHz | Music in general (the tool's default) |
| 256 kbps | 1.92 MB | 115.2 MB | 19.7 kHz | 20.5 kHz | When the source is AAC at 256 kbps or more |
| 320 kbps | 2.40 MB | 144.0 MB | 20.5 kHz | 20.5 kHz | The highest MP3 bitrate |
Sizes assume 44.1 kHz. A real file is a little larger because of its tags and cover art. In mono, LAME raises the low-pass frequency by a factor of 1.5. White noise encoded with LAME at 64 kbps mono kept content up to about 16.7 kHz (measured 2026-10-20).
Real results from the sample file
These are the actual results of converting the sample file "Morning Walk" (20 seconds, about 242 kbps AAC, 44.1 kHz stereo, with cover art, 612 KB) at each step. Up to 192 kbps the MP3 is smaller than the original. From 256 kbps up it is larger.
| Bitrate | MP3 size | Compared with the original |
|---|---|---|
| 64 kbps | 164 KB | 27% |
| 96 kbps | 244 KB | 40% |
| 128 kbps | 325 KB | 53% |
| 192 kbps | 485 KB | 79% |
| 256 kbps | 646 KB | 106% (larger) |
| 320 kbps | 807 KB | 132% (larger) |
The original is about 242 kbps AAC, so 256 and 320 kbps make the file larger than the source without sounding better than it. The sound cannot get better than the source. For this file the highest step that is still smaller than the original is 192 kbps.
Why a bitrate above the original does not help
An M4A made with AAC has already thrown away part of the sound. A higher MP3 bitrate shrinks the new loss that re-encoding adds, but it cannot bring back what was already removed. Apple gives the same advice: converting between compressed formats may reduce quality, and for the best results you should re-import the music from the original source in the new format.
- If the source is AAC at 128 kbps, MP3 at 320 kbps makes a file 2.5 times larger without adding any sound that was not there. When your choice is higher than the source, the tool says so under the ladder.
- If the source is ALAC (lossless), the MP3 is a lossy copy at every step. Keep the original for archiving and use the MP3 for listening and sharing.
- The most reliable way to decide whether a low bitrate is good enough is to listen. After converting, use "Listen" to switch between the original and the MP3 at the same position.
Converting voice memos and recordings
- For speech only, use the Voice preset (mono 64 kbps), which comes to about 0.48 MB a minute. If every file you add is mono at 96 kbps or lower, the tool picks this setting for you first.
- Exporting an iPhone voice memo to the Files app gives an .m4a by default, with layered recordings flattened and Spatial Audio turned into stereo. You can drop that file in as it is.
- The Voice Memos app on a Mac has an Audio Quality setting with Compressed (smaller files) and Lossless (larger files). A lossless recording shows up here as ALAC, and converting it to MP3 makes it much smaller.
- If you do not want a title or album in the file you send, turn off "Keep tags and cover art" before converting. With it off, the MP3 gets no tags at all.
How tags and cover art carry over
With "Keep tags and cover art" on, the title, artist, album, album artist, year, genre and similar tags from the M4A are written to the MP3 as ID3v2.3 tags, and the cover art (JPEG or PNG) is added as the front cover. The list shows each file's cover on the left and its artist and title next to the name, so you can see what will carry over before you convert.
Chapters, such as the chapter marks in an M4B audiobook, are not carried over either way. The MP3 is named after the original with .mp3 added, and if that name is taken it gets a number, as in "(2)".
Common mistakes
- Renaming the file to .mp3: this changes only the name. The audio inside is still AAC, so a device or site that accepts only MP3 will still refuse it.
- Thinking 320 kbps beats the original: it does not improve the sound, and the file just grows. Steps above the original's size on the ladder get an ↑ mark.
- Expecting mono to halve the size: at the same bitrate the size is the same. To make the file smaller, lower the bitrate.
- Older iTunes Store songs (.m4p): files with copy protection (DRM) cannot be converted. Apple's Music help also says only iTunes Plus songs can be converted. The tool lists such files with the reason and skips them.
- 5.1 surround audio: MP3 supports only two channels, so the sound is mixed down to stereo.
Limits and things to know
- You can add 20 files at a time, up to 100 MB each, and they convert one after another. A large file can fail if your device runs low on memory.
- The first conversion downloads the converter engine (ffmpeg.wasm, FFmpeg compiled to WebAssembly, about 32 MB). It is not downloaded again while it stays in your browser cache.
- Only constant-bitrate (CBR) MP3 is produced. Variable bitrate (VBR) is not an option.
- Files at 32, 44.1 or 48 kHz keep their sample rate. Anything else, such as 22.05 kHz, is saved at 44.1 kHz. Those three are the rates at which MP3 (MPEG-1 Layer III) can use every bitrate from 32 to 320 kbps.
- The sizes on the ladder are estimates at 44.1 kHz. After converting, the real size is shown.
- Listening to the original works only if your browser can play that format. ALAC has weak browser support, so you may have to convert first and listen to the MP3.
- Converted MP3s disappear when you reload the page or remove them from the list, so save them first.
Checked on Sources and example results were verified on 2026-10-20.
Sources
- 01MDN: Web audio codec guideAAC is lossy, ALAC is lossless with weak browser support, and MP3 (MPEG-1) runs at 32, 44.1 and 48 kHz with 32 to 320 kbps
- 02MDN: Digital audio conceptsHumans can hear sounds up to 20,000 Hz
- 03Library of Congress: AAC_MP4The file extension for AAC follows the container, and MPEG-4 audio files use mp4 or m4a
- 04Library of Congress: MP3Perceptual coding that discards or reduces the precision of components the ear notices less
- 05Apple Support: Share voice memo recordings on iPhoneRecordings are exported as .m4a by default; layered recordings are flattened and Spatial Audio becomes stereo
- 06Apple Support: Change Voice Memos settings on MacAudio Quality: Compressed (smaller files) or Lossless (larger files)
- 07Apple Support: Convert music file formats in Music on MacConverting between compressed formats (MP3 and AAC) may reduce quality; iTunes Store purchases convert only if they are iTunes Plus songs
- 08LAME: libmp3lame/lame.cLow-pass frequency by bitrate (lowpass_by_bitrate): 11,000 Hz at 64 kbps up to 20,500 Hz at 320 kbps
- 09FFmpeg documentation: mp3 muxerWrites ID3v2.3 and 2.4 tags and cover art (APIC); the constant bitrate (b) option for libmp3lame is in the ffmpeg-codecs documentation
- 10ffmpeg.wasm: FAQ2 GB input limit (WebAssembly); @ffmpeg/ffmpeg is MIT and @ffmpeg/core carries the FFmpeg license (GPL-2.0 or later). This tool uses 0.12.15 and 0.12.10
- 11Fraunhofer IIS: mp3The Technicolor and Fraunhofer IIS mp3 licensing program ended on April 23, 2017
Frequently asked questions
Are my M4A files uploaded to a server?
No. The converter engine (about 32 MB) downloads once, and everything after that, from reading the file to making the MP3, happens inside this browser. The MP3s are created on your device and saved with the Save button.
What bitrate should I use?
192 kbps is a solid starting point for music and mono 64 kbps for voice recordings. A bitrate above the original won't sound better than the source and makes the file bigger, so stay at or below the source bitrate shown in the list and check by ear with Listen.
Does 320 kbps sound better than the original?
No. Sound that AAC already discarded does not come back when you re-encode to MP3. A higher bitrate only reduces the new loss that re-encoding adds, and choosing more than the original just makes the file larger.
Will the MP3 be smaller than the M4A?
It depends on the bitrate you pick. MP3 size is bitrate times length, so a bitrate above the source AAC makes the file larger. The 612 KB sample file becomes 485 KB at 192 kbps and 807 KB at 320 kbps.
Can I convert an iPhone voice memo to MP3?
Yes. Exporting a voice memo to the Files app gives you an .m4a file by default, so just add that file. For speech, the tool picks mono 64 kbps first, which is about 0.48 MB per minute.
Are the title, artist and cover art kept?
With "Keep tags and cover art" on, title, artist, album, year and genre are written as ID3v2.3 tags and the cover art becomes the front cover. Turn it off and the MP3 has no tags at all. Audiobook chapters are not carried over.
Does mono cut the file size in half?
No. MP3 size is set by the bitrate, so mono and stereo files at the same bitrate are the same size. To shrink the file, lower the bitrate, and for speech use mono so those bits go to a single channel.
Are there M4A files that cannot be converted?
Yes: older iTunes Store songs with copy protection (.m4p), files with no audio track, and damaged files. The list shows the reason and skips them. Files over 100 MB are not added.