Duration in, file size out — for every common recording format. Runs entirely in your browser.
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Uncompressed size = sample rate × bit depth × channels × seconds ÷ 8. Compressed size = bitrate × seconds ÷ 8.
Real lossy files vary a few percent with container overhead and VBR. See the
bitrate, sample rate and
bit depth glossary entries for the mechanics, or the
format encyclopedia for what each container holds.