Free converter · Lossy re-encode
Convert AAC to MP3
Short answer
Drop your AAC file into the converter below and download the MP3 file. It runs in your browser with FFmpeg, for files up to 100 MB; nothing is uploaded. The file is re-encoded to MP3 audio at about 128 kbps, keeping the source's sample rate. Re-encoding takes longer than a container swap and costs some quality; how much depends on the clip and on the quality setting, and at the converter's default setting the loss can be visible, so keep the original.
Maximum file size: 100 MB. The first conversion loads a ~30 MB converter engine, once per visit. Nothing is uploaded - conversion runs on your device.
Both lossy; quality depends on source bitrate and encoder. · Lossy re-encode · Browser-side via FFmpeg WASM - nothing uploaded.
Key takeaways
- The 245 KB AAC file became a 161 KB MP3 file (-34.2%), about 128 kbps for the 10 second clip.
- The result holds: Audio: mp3 48000 Hz 2 ch.
- In your browser the same conversion of a 3 second clip took 0.12 seconds on the single-thread engine; natively, the 10 second clip took 0.24 seconds.
- Next to it: AAC to FLAC (+567%), AAC to M4A (-0.3%), AAC to OGG (-51.2%).
Measured: AAC to MP3
The converter's own ffmpeg arguments, run on a 10 second 1920 × 1080 excerpt of Big Buck Bunny (an animated film, not camera footage) saved in AAC. The browser column is the same arguments on the single-thread WebAssembly core with a 3 second excerpt, in a headless run; your device will differ. Results describe this clip and these encoders.
| Check | Result |
|---|---|
| Mode | Audio re-encoded |
| Input | AAC, 245 KB |
| Output | MP3, 161 KB (-34.2%) |
| Output streams | Audio: mp3 48000 Hz 2 ch |
| Time, native, 10 s clip | 0.24 s |
| Time, browser engine, 3 s clip | 0.12 s |
A re-encode decodes and encodes every frame or sample, so the time grows with the length of the file.
AAC vs MP3
| AAC | MP3 | |
|---|---|---|
| Full name | Advanced Audio Coding (raw stream) | MPEG-1 Audio Layer III |
| What is inside | AAC audio without a container | MP3 audio |
| Compression | Lossy | Lossy |
| Best for | Players that take a bare AAC stream; M4A is the more common wrapper | Music and podcasts that must play on every device |
What you get
MP3 audio at about 128 kbps, keeping the source's sample rate. Both lossy; quality depends on source bitrate and encoder.
Planning a bigger file
These are estimates scaled up from the 10 second clip. Real files differ with content, resolution and bitrate, so treat them as an order of magnitude, not a promise.
| Length of the video or recording | Input size (like ours) | MP3 size | Time in your browser |
|---|---|---|---|
| 1 minute | 1.46 MB | 961 KB | 2 seconds |
| 10 minutes | 14.62 MB | 9.61 MB | 24 seconds |
| 1 hour | 87.70 MB | 57.68 MB | 2.4 minutes |
An AAC file of this kind reaches the 100 MB limit of the converter after about 72 minutes; converting it would take roughly 2.9 minutes on the single-thread engine, and the MP3 would be about 68.97 MB.
AAC and MP3 next to their neighbors
The same clip through other conversions with the same source or the same target.
| Conversion | How | Size change | Time (native) |
|---|---|---|---|
| AAC to MP3 | Re-encode | -34.2% | 0.24 s |
| AAC to FLAC | Re-encode | +567% | 0.11 s |
| AAC to M4A | Copy | -0.3% | 0.05 s |
| AAC to OGG | Re-encode | -51.2% | 0.22 s |
| AAC to Opus | Re-encode | -52.3% | 0.10 s |
| AAC to WAV | Re-encode | +686% | 0.09 s |
| AIFF to MP3 | Re-encode | -91.6% | 0.23 s |
Choosing MP3
MP3: MPEG-1 Audio Layer III. Music and podcasts that must play on every device. AAC: Advanced Audio Coding (raw stream). Players that take a bare AAC stream; M4A is the more common wrapper.
- Keep your original: a re-encode is a copy of a copy.
- If the destination states the format it accepts, use that and nothing else.
Questions people ask
Is this AAC to MP3 converter free and private?
Yes. It is free, needs no account and runs entirely in your browser, so the file never leaves your device.
Will converting AAC to MP3 reduce quality?
Some, because MP3 is lossy and the file is re-encoded. How much depends on the clip and on the quality setting, and at the converter's default setting the loss can be visible, so keep the original. For uploads, the platform re-encodes again anyway.
Is there a file size limit?
Files up to 100 MB. The first conversion downloads a converter engine of about 30 MB once per visit; larger files are better handled by a desktop app such as HandBrake or FFmpeg.
How do I convert AAC to MP3?
Choose the file in the converter above and download the MP3. It runs in your browser with no upload.
Will converting AAC to MP3 reduce quality?
A little, because MP3 is lossy. Keep the original file.
Why did the file size change by -34.2%?
The target codec and settings decide the size. This 10 second clip came out at 161 KB, about 128 kbps.
How long does it take?
A 3 second clip took 0.12 seconds in the browser engine in our test; time grows with the length of the file.
How long will an AAC file of 100 MB take?
At the speed we measured in the browser engine, about 2.9 minutes for a file like our clip. Your device and the content will change it.
Is my file uploaded?
No. The conversion runs in your browser.
Is there a size limit?
Files up to 100 MB. The first conversion downloads a converter engine of about 30 MB once per visit.
More converters
Sources and how we checked
- MDN: Media container formats
- MDN: Web audio codec guide
- MDN: Image file type and format guide
- FFmpeg documentation: stream copy
- FFmpeg Documentation: ffmpeg (stream selection, -map, -c copy) (read 2026-10-09)
- MDN: Web audio codec guide (read 2026-10-09)
- Blender Foundation: Big Buck Bunny (CC BY 3.0), the clip used for the measurements (read 2026-10-09)
Reviewed October 8, 2026. What the converter writes was measured with ffprobe on the same FFmpeg build your browser downloads; format descriptions follow MDN's media guides.