AAC vs MP3: which should you use?
Both shrink audio by leaving out detail you are unlikely to hear. AAC is the newer, more efficient format; MP3 plays on more old hardware. We encoded the same minute of music in both to show what actually changes.
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Quick answer: AAC and MP3 files are the same size at the same bitrate: one minute of music came to 0.98 MB as 128 kbps AAC and 0.96 MB as 128 kbps MP3. The difference is quality per bit. AAC keeps more detail at 128 kbps and below; at 256 kbps and above most people hear no difference from the original in either. Use AAC for phones and streaming, MP3 for old car stereos and players.
Updated
Choose AAC when
- The file is for an iPhone, Android phone, Apple Music or a video.
- You want small files at low bitrates, such as voice recordings or podcasts at 64–96 kbps.
- The audio will go inside an MP4 video: AAC is the standard sound format there.
Choose MP3 when
- It has to play on an old car stereo, MP3 player or anything you are unsure about.
- Someone asks for "an MP3" by name, such as a podcast host or a teacher.
- You use 192 kbps or more, where the quality gap closes.
Same minute of music, measured
| Format | Bitrate | Size |
|---|---|---|
| MP3 | 128 kbps | 0.96 MB |
| AAC (.m4a) | 128 kbps | 0.98 MB |
| MP3 | 192 kbps | 1.44 MB |
| AAC (.m4a) | 256 kbps | 1.93 MB |
| MP3 | 320 kbps | 2.40 MB |
| WAV (original) | 1,411 kbps | 10.58 MB |
One minute of the Sintel trailer soundtrack (stereo, 44.1 kHz), made with standard free software on 20 October 2026. Sintel © Blender Foundation, CC BY 3.0.
How it works
- Drop your audio fileM4A, WAV, FLAC, OGG and more, any length. It stays on your computer.
- Pick the quality"Very good" suits speech and most music; "Best" for music you care about.
- Download the MP3Plays on every phone, computer, car stereo and audio editor.
The bitrate sets the size, the format sets the quality
A lossy file's size is its bitrate times its length, whatever the format: 128 kbps is about 0.96 MB a minute in MP3, AAC or Opus alike. What the format changes is how good those bits sound. AAC, designed later than MP3, spends them more cleverly, so it sounds cleaner at the same bitrate, most clearly at 128 kbps and below. At 256 kbps, the rate Apple sells music at, both are very hard to tell from the original.
.aac, .m4a and AAC inside videos
AAC is the sound format; .m4a is the usual file it lives in, used by iPhone Voice Memos, iTunes and many recorders. A bare .aac file is the same sound without the M4A wrapper, common from screen recorders and radio streams. The sound in almost every MP4 video is AAC as well.
Converting between them
Each lossy conversion throws away a little more, so convert only when a device or site needs the other format, and keep the original. Going from AAC to MP3, pick a bitrate at or above the original's: 128 kbps AAC is best kept as 192 kbps MP3. The converter above does that in your browser; nothing is uploaded.
Measured, not promised
From our tests in Chrome on a 2019 Intel MacBook, October 2026. See all results.
Why your audio never leaves your computer
Online converters upload your file to their servers, convert it there and send it back. That is slow for long recordings, so free plans cap the length or the number of files, and your recording sits on someone else's computer.
Here your own computer does the work, inside this tab. Nothing is uploaded, so there is nothing to cap: no length limit, no daily limit and no sign-up.
Questions
Is 320 kbps MP3 better than 256 kbps AAC?
In practice they are equal: at those rates most people cannot tell either from the original. The 320 kbps MP3 is about a quarter bigger.
Will converting AAC to MP3 improve the sound?
No. A conversion cannot bring back detail the AAC left out; it can only keep what is there, at a high enough bitrate.
Which plays on more devices?
MP3. AAC plays on every phone and computer made in the last fifteen years or so, but some older car stereos and MP3 players only take MP3.
Can I convert several files at once?
Yes. Choose or drop several files together. They are converted one after another with the same settings, and you can download each one or all of them in one ZIP.
Is it really free?
Yes. Your computer does the work, so a file costs us nothing to convert. No account and no limits.
Is my file uploaded?
No. It is converted inside this browser tab and saved straight back to your computer.
Which browsers work?
Recent Chrome, Edge and Safari on a computer.
Can I use a video file?
Yes. Drop a video and you get its sound.