Bitrate to File Size Calculator
Calculate compressed audio file size (MP3, AAC, OGG) from bitrate in kbps and track duration.
How to use this tool
- Enter bitrate and duration in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your file size and the full breakdown beneath it.
Calculate how much storage space a compressed audio track will use given its bitrate and duration.
⚠ This tool provides general estimates for education only and is not financial, tax or legal advice. Figures may not reflect your situation — verify with a qualified professional.
Formula
File size (MB) = bitrate (kbps) × 1000 × duration (s) ÷ 8 ÷ 1 048 576
File size (KB) = file size (MB) × 1024
How it works
This calculator estimates the size of a compressed audio file — such as MP3, AAC, or OGG Vorbis — from its constant bitrate and duration. It converts kilobits per second to bytes and scales by the track length in seconds.
Results are accurate for constant-bitrate (CBR) encodes. Variable-bitrate (VBR) files vary in size because the encoder allocates more bits to complex passages; this calculator provides a good approximation for VBR by using the average target bitrate.
Worked example
- Bitrate = 320 kbps, duration = 3 minutes = 180 s.
- Total bits = 320 × 1000 × 180 = 57 600 000 bits.
- File size = 57 600 000 / 8 / 1 048 576 ≈ 6.87 MB.
- In KB: 6.87 × 1024 ≈ 7 034 KB.
File size: 6.87 MB
Common mistakes to avoid
- Confusing bitrate in kbps with kilobytes per second; 128 kbps = 128 000 bits/s = 16 KB/s, not 128 KB/s.
- Using this formula for lossless formats like FLAC or ALAC, which have variable bitrate; the result will be inaccurate.
- Forgetting that container overhead (ID3 tags, metadata) adds bytes beyond the raw audio bitrate calculation.
Key terms
- Bitrate (kbps)
- Kilobits per second; the amount of compressed audio data stored or streamed per second. Common MP3 bitrates are 128, 192, and 320 kbps.
- CBR (Constant Bitrate)
- An encoding mode where the bitrate stays fixed throughout the file, making file size directly proportional to duration.
- VBR (Variable Bitrate)
- An encoding mode that allocates more bits to complex audio passages and fewer to simple ones, typically achieving better quality at a given average file size.
- Lossy compression
- Audio compression that permanently discards inaudible or less perceptible audio data to reduce file size. MP3, AAC, and OGG use lossy compression.
- Mebibyte (MB)
- As used here, 1 MB = 1 048 576 bytes (binary definition). File managers and operating systems may display sizes using this binary unit.
Frequently asked questions
- How large is a 3-minute MP3 at 320 kbps?
- Approximately 6.87 MB. At 128 kbps the same track would be around 2.75 MB.