Audio File Size Calculator
Work out the size of an audio file from its bitrate and duration — for MP3, AAC, streaming or podcast planning.
How it works
Bytes = bitrate (kbps) × 1000 × seconds ÷ 8
Audio bitrate is measured in kilobits per second, so the file size is simply the bitrate times the length in seconds, converted from bits to bytes by dividing by 8. A constant-bitrate (CBR) file follows this exactly; variable-bitrate (VBR) files vary around the average, so treat the result as an estimate. Higher bitrates mean better fidelity and proportionally larger files.
Worked example
A 3.5-minute (210-second) track at 320 kbps: 320 × 1000 × 210 ÷ 8 = 8,400,000 bytes ≈ 8.4 MB. Each minute adds 320 × 1000 × 60 ÷ 8 = 2.4 MB.
Frequently asked questions
What bitrate should I use for music?
For MP3, 128 kbps is acceptable, 192–256 kbps is good, and 320 kbps is near-transparent. Modern codecs like AAC or Opus sound as good at lower bitrates, so 128–192 kbps AAC rivals 320 kbps MP3.
Why is my file a slightly different size?
Container overhead (ID3 tags, cover art, headers) adds a little, and variable-bitrate encoding fluctuates around the nominal rate. The formula gives the audio-stream size for constant bitrate; real files land within a few percent.
How big is an hour-long podcast?
At a typical 64 kbps mono spoken-word rate: 64 × 1000 × 3600 ÷ 8 = 28.8 MB per hour. Bump to 128 kbps stereo and it doubles to about 57.6 MB.
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This calculator is for educational purposes. Double-check important results before acting on them.