Key takeaways
- File size = kbps × 1,000 × seconds ÷ 8: 4.1 MB for 192 kbps over three minutes.
- Checked on real files: 10 seconds of audio at a set bitrate came out +0.6%, +2.1%, -1.0%, +5.7% from the formula (MP3, AAC, Opus, WMA); the difference is framing and metadata.
Choosing a bitrate
At a set bitrate the file size depends only on the length: 192 kbps is 1.4 MB a minute. A higher bitrate makes a bigger file and, up to a point, a better sound; speech needs far less than music.
The comparison with a CD-quality WAV shows what compression buys. It is not a quality score: two files of the same size can sound different.
Scenarios
| Scenario | Audio file size | Per minute | Compression versus that WAV |
|---|---|---|---|
| 128 kbps, 3 minutes | 2.7 MB | 938 KB | 11.0× smaller |
| 192 kbps, 3 minutes | 4.1 MB | 1.4 MB | 7.3× smaller |
| 320 kbps, 3 minutes | 6.9 MB | 2.3 MB | 4.4× smaller |
| 64 kbps voice, 30 minutes | 13.7 MB | 469 KB | 22.0× smaller |
| 96 kbps, 1 hour podcast | 41.2 MB | 703 KB | 14.7× smaller |
Measured: formula against real files
The same 10 second soundtrack encoded at a stated bitrate in four formats with ffmpeg 6.1.1.
| Format | Bitrate set | Formula | Real file | Difference |
|---|---|---|---|---|
| MP3 | 192 kbps | 240 KB | 242 KB | +0.6% |
| AAC (ADTS) | 192 kbps | 240 KB | 245 KB | +2.1% |
| Opus | 128 kbps | 160 KB | 158 KB | -1.0% |
| WMA | 192 kbps | 240 KB | 254 KB | +5.7% |