Audio Bitrate / File Size Estimator
Estimate audio file size from duration and bitrate.
Overview
The audio bitrate and file size estimator predicts how large an audio file will be once you've picked a codec, bitrate, and duration. Drop in a track length and a target bitrate (say, 192 kbps MP3 or 320 kbps AAC) and the tool returns the expected file size in megabytes, plus how long that fits into a given storage budget.
It's a quick sanity check for podcasters batching episodes, musicians distributing album previews, and engineers planning bandwidth for streaming services or on-device audio assets. Knowing the math up front prevents surprises when you upload to a CDN, attach to email, or burn to physical media with hard size caps.
How it works
Audio file size for a constant bitrate (CBR) stream is a tidy linear formula: size in bits equals bitrate (bits per second) multiplied by duration (seconds). Divide by eight to get bytes and again by 1024 twice to convert to mebibytes. So a 4-minute song at 192 kbps weighs in at roughly 192,000 x 240 / 8 = 5.76 MB, plus a few kilobytes of container and tag overhead.
Variable bitrate (VBR) encoders complicate this slightly because the bitrate fluctuates with audio complexity, but the average bitrate stamped in the file header gives a close estimate. Lossless formats like FLAC or ALAC depend on the source's entropy and typically land at 50-70 percent of uncompressed PCM (1,411 kbps for CD-quality stereo).
Examples
Duration: 3:30, Bitrate: 128 kbps → 3.36 MB
Duration: 60:00 podcast, Bitrate: 64 kbps mono → ~28.8 MB
Duration: 45:00, Bitrate: 320 kbps stereo → ~108 MB
Duration: 4:00, FLAC ~900 kbps avg → ~27 MB
FAQ
Does the calculation include ID3 tags and album art?
No, those add a small fixed overhead (typically under 100 KB unless you embed high-resolution artwork). For most planning purposes you can ignore them.
Why does my actual MP3 file differ from the estimate?
CBR files match the formula closely. VBR files vary because the encoder spends fewer bits on silence and simpler passages. Use the file's reported average bitrate for the most accurate estimate.
What bitrate should I pick for spoken word versus music?
Spoken word stays clean at 64-96 kbps mono. Music typically uses 192-320 kbps stereo for transparent quality, or 128 kbps for casual listening with smaller files.
How is uncompressed PCM size calculated?
Sample rate x bit depth x channels x duration. CD-quality stereo is 44,100 x 16 x 2 = 1,411,200 bits per second, or about 10 MB per minute.