What Is MP3 Bitrate?
Bitrate is the amount of data used for each second of audio, measured in kilobits per second (kbps). Common MP3 bitrates are 128, 192, 256 and 320 kbps; 320 is the maximum. More bits mean the encoder throws away less sound, and the file gets bigger.
MP3 can be encoded two ways. CBR (constant bitrate) uses the same bitrate for every second. VBR (variable bitrate) spends more bits on complex passages and fewer on simple ones. VBR presets are named V0 (highest) to V9 (lowest).
Why AAC-to-MP3 Is Different from Lossless Sources
When you convert from WAV or FLAC to MP3, the encoder works with the complete original signal. Converting from AAC is different — the audio has already been through one round of lossy compression. The MP3 encoder is working on data that's already had information removed.
This generation loss means the MP3 output can never sound better than the AAC source. The goal is to preserve as much of the remaining quality as possible by choosing the right bitrate.
Key rule: Never exceed your source AAC bitrate by more than ~25%. Converting a 128 kbps AAC to 320 kbps MP3 just inflates the file — the extra bits have nothing to fill. Match or slightly exceed the source bitrate for optimal results.
How to Match Your AAC Source Bitrate
Common AAC bitrates and the recommended MP3 settings:
| AAC Source | Common Origin | Recommended MP3 | Why |
|---|---|---|---|
| 64 kbps | Voice memos, low-quality streams | CBR 128 kbps | MP3 needs slightly higher bitrate to match AAC quality |
| 128 kbps | Spotify Free, older iTunes | VBR V4 (~165 kbps) | VBR compensates for MP3's lower efficiency vs AAC |
| 192 kbps | Streaming services | VBR V2 (~190 kbps) | Matches average bitrate, VBR quality exceeds CBR equivalent |
| 256 kbps | iTunes Store, Apple Music downloads | VBR V0 (~245 kbps) | Best match for high-quality AAC sources |
| 320 kbps | Spotify Premium (OGG, but similar) | CBR 320 kbps | Maximum MP3 bitrate for high-bitrate sources |
CBR Bitrate Comparison: 128 vs 192 vs 256 vs 320
Here's how each Constant Bit Rate level compares for a typical 4-minute song:
| CBR Bitrate | File Size (4 min) | Quality | Best For |
|---|---|---|---|
| 128 kbps | 3.84 MB | Acceptable | Speech, podcasts, low-bitrate AAC sources |
| 192 kbps | 5.76 MB | Good | General listening, mid-bitrate AAC sources |
| 256 kbps | 7.68 MB | Very good | iTunes 256k AAC sources, music collections |
| 320 kbps | 9.6 MB | Excellent | High-bitrate sources, maximum MP3 quality |
VBR: Better Quality at Smaller Sizes
Variable Bit Rate encoding allocates bits dynamically — more for complex passages, fewer for silence. This is especially valuable for AAC-to-MP3 conversion because the encoder can spend extra bits on passages where lossy-to-lossy degradation is most noticeable.
| VBR Preset | Avg Bitrate | File Size (4 min) | Best For |
|---|---|---|---|
| V0 | ~245 kbps | ~7.2 MB | 256 kbps AAC sources (iTunes Store) |
| V2 | ~190 kbps | ~5.5 MB | General use (recommended default) |
| V4 | ~165 kbps | ~4.8 MB | 128 kbps AAC sources, podcasts |
| V6 | ~130 kbps | ~3.8 MB | Voice recordings, low-quality sources |
Recommendation: VBR V2 is the default for most conversions. If your AAC source is 256 kbps from iTunes, step up to VBR V0 for the best result. For a deeper comparison of VBR and CBR encoding methods, see our VBR vs CBR guide.
AAC vs MP3: Why You Might Need to Convert
AAC (Advanced Audio Coding) is technically a better codec than MP3 — it produces higher quality at the same bitrate, especially below 128 kbps. So why convert to MP3?
- Device compatibility: Some car stereos, older media players, and embedded systems only support MP3
- Software requirements: Certain audio tools, DJ software, or games require MP3 input
- Universal playback: MP3 is supported by every device and player ever made
- Sharing: MP3 is the most widely recognized audio format — recipients won't have compatibility issues
The quality difference between AAC and MP3 at 192+ kbps is minimal in practice. If you need MP3 for compatibility, the conversion is worth it. For choosing whether to normalize volume during conversion, see the loudness normalization guide.
MP3 File Size by Bitrate
File size = bitrate × duration ÷ 8. A 320 kbps MP3 stores 320,000 bits per second, which is 40 KB per second or 2.4 MB per minute.
| Bitrate | 1 minute | 4-minute song | 1 hour |
|---|---|---|---|
| 128 kbps | 0.96 MB | 3.84 MB | 57.6 MB |
| 192 kbps | 1.44 MB | 5.76 MB | 86.4 MB |
| 256 kbps | 1.92 MB | 7.68 MB | 115.2 MB |
| 320 kbps | 2.4 MB | 9.6 MB | 144 MB |
Sizes are in decimal megabytes (1 MB = 1,000,000 bytes) and exclude cover art and tags. VBR files vary with the music.
Bitrate vs Sample Rate vs Bit Depth
- Sample rate (44.1 kHz, 48 kHz) is how many times per second the sound is measured.
- Bit depth (16-bit, 24-bit) is how precisely each measurement is stored. It matters for WAV and FLAC; MP3 does not store a bit depth.
- Bitrate is the result for compressed files: how much data the encoder keeps per second. For MP3 it is the setting that decides quality and size.
How to Change MP3 Bitrate
- CleverUtils: in the converter above, choose CBR 128, 192, 256 or 320 kbps, or VBR V0, V2, V4 or V6.
- Audacity: File → Export Audio, choose MP3, then set Bit Rate Mode and Quality.
- FFmpeg:
ffmpeg -i input.m4a -codec:a libmp3lame -b:a 192k output.mp3for CBR, or-q:a 2instead of-b:afor VBR V2.
Raising the bitrate does not restore quality. Re-encoding a 128 kbps file at 320 kbps gives a bigger file that sounds the same as the 128 kbps source or slightly worse.