Bitrate is measured in kilobits per second (kbps). A 320 kbps MP3 uses 320,000 bits for every second of sound, which is 2.4 MB per minute. Halve the bitrate and you halve the file size.
Lossless formats work differently: their bitrate follows the music, because FLAC and ALAC compress each recording as tightly as they can without losing anything.
Recommended bitrates
| Use | MP3 | AAC / M4A | Opus |
|---|---|---|---|
| Music, best quality | 320 kbps | 256 kbps | 160 kbps |
| Music, everyday listening | 192–256 kbps | 160–192 kbps | 128 kbps |
| Podcasts and speech | 96–128 kbps | 64–96 kbps | 48–64 kbps |
| Voice memos | 64 kbps mono | 48 kbps | 24–32 kbps |
Bitrate and file size
File size = bitrate × duration. A 4-minute song is about 9.6 MB at 320 kbps, 5.8 MB at 192 kbps and 3.8 MB at 128 kbps. Uncompressed CD-quality WAV runs at 1411 kbps, about 42 MB for the same song.
SoundBench's Audio Calculator works these out for any duration, and Reduce File Size can pick the bitrate for a target size automatically.
Sample rate and bit depth are different things
Sample rate (44.1 or 48 kHz) sets the highest frequency that can be stored. Bit depth (16 or 24-bit) sets the dynamic range. Bitrate is the data rate after compression. For listening, 16-bit / 44.1 kHz covers the full range of human hearing; 24-bit is most useful while recording and mixing.
Constant vs variable bitrate
Constant bitrate (CBR) uses the same amount of data every second, which makes file size predictable. Variable bitrate (VBR) gives more data to complex passages and less to simple ones, often giving better quality for the same average size.
Frequently asked questions
Is a higher bitrate always better?
Up to a point. Above about 256 kbps AAC or 320 kbps MP3, most people cannot hear any further improvement, but the files keep getting bigger.
Does re-encoding at a higher bitrate improve quality?
No. Converting a 128 kbps MP3 to 320 kbps makes the file bigger without restoring anything.
What bitrate do streaming services use?
Typical tiers are about 96 to 160 kbps for normal quality and 256 to 320 kbps for high quality. Lossless tiers stream FLAC or ALAC at roughly 700 to 1000 kbps for CD quality.