The Formula
MP3 file size can be calculated precisely for CBR (Constant Bit Rate) files:
File Size (MB) = Bitrate (kbps) × Duration (seconds) ÷ 8 ÷ 1,024
Breaking it down:
- Bitrate is in kilobits per second (e.g., 320 kbps)
- Divide by 8 to convert bits to bytes
- Divide by 1,024 to convert kilobytes to megabytes
Example: a 4-minute song at 320 kbps = 320 × 240 / 8 / 1,024 = 9.38 MB
File Size by Bitrate and Duration
| Bitrate | 3 min | 5 min | 30 min | 1 hour | 2 hours |
|---|---|---|---|---|---|
| 64 kbps | 1.4 MB | 2.3 MB | 14.1 MB | 28.1 MB | 56.3 MB |
| 96 kbps | 2.1 MB | 3.5 MB | 21.1 MB | 42.2 MB | 84.4 MB |
| 128 kbps | 2.8 MB | 4.7 MB | 28.1 MB | 56.3 MB | 112.5 MB |
| 192 kbps | 4.2 MB | 7.0 MB | 42.2 MB | 84.4 MB | 168.8 MB |
| 256 kbps | 5.6 MB | 9.4 MB | 56.3 MB | 112.5 MB | 225.0 MB |
| 320 kbps | 7.0 MB | 11.7 MB | 70.3 MB | 140.6 MB | 281.3 MB |
VBR File Sizes (Approximate)
VBR files vary in size because the bitrate changes per frame. These are typical averages:
| LAME Preset | Avg Bitrate | 4-min Song | 1-hour Podcast |
|---|---|---|---|
| V0 | ~245 kbps | ~7.2 MB | ~108 MB |
| V2 | ~190 kbps | ~5.6 MB | ~84 MB |
| V4 | ~165 kbps | ~4.8 MB | ~73 MB |
| V6 | ~115 kbps | ~3.4 MB | ~51 MB |
Note: VBR sizes depend on audio complexity. A quiet speech recording at V2 may average 150 kbps, while a dense orchestral recording at V2 may average 220 kbps. The values above are typical for popular music.
How Many Songs Fit on Your Device?
Assuming an average song length of 4 minutes:
| Storage | 128 kbps | 192 kbps | 256 kbps | 320 kbps |
|---|---|---|---|---|
| 1 GB | ~266 | ~170 | ~133 | ~106 |
| 8 GB | ~2,130 | ~1,360 | ~1,060 | ~850 |
| 16 GB | ~4,260 | ~2,720 | ~2,130 | ~1,700 |
| 64 GB | ~17,000 | ~10,900 | ~8,500 | ~6,800 |
| 256 GB | ~68,000 | ~43,500 | ~34,000 | ~27,200 |
Podcast Storage Planning
Podcasts are typically mono at lower bitrates. Storage needs accumulate fast across episodes:
| Setting | 1 Episode (1h) | 50 Episodes | 200 Episodes |
|---|---|---|---|
| 64 kbps mono | 28 MB | 1.4 GB | 5.5 GB |
| 96 kbps mono | 42 MB | 2.1 GB | 8.2 GB |
| 128 kbps stereo | 56 MB | 2.8 GB | 11.0 GB |
| 192 kbps stereo | 84 MB | 4.1 GB | 16.4 GB |
Industry standard: Apple Podcasts recommends 96 kbps CBR mono. At this setting, a weekly 1-hour show generates about 2.1 GB per year (50 episodes). See our podcast settings guide for full specifications.