How audio bitrate calculator works
Bitrate and duration fully determine an audio file’s size: bytes = kbps × 1,000 ÷ 8 × seconds. Bitrates are quoted in kilobits per second (SI — 1 kbps is exactly 1,000 bit/s), so a 320 kbps MP3 writes 40,000 bytes every second, and a 3:30 track is 210 s × 40,000 = 8.4 MB. Enter a bitrate and a duration and the panel shows the exact byte count plus both size formats side by side.
The two size formats disagree on purpose. SI megabytes (MB, ×1,000 per step) are what storage vendors and download pages quote; binary mebibytes (MiB, ×1,024 per step) are what most operating systems report. The same 8.4 MB file reads as 8.01 MiB — a 4.9% gap that is pure convention, not missing data. For planning, the per-minute and per-hour rates matter more: 320 kbps is 2.4 MB per minute or 144 MB per hour, and the copies field multiplies that by however many episodes, stems or backups you keep.
The inverse modes answer the reverse questions. Hand it a file size and a duration and it reports the bitrate the file actually delivers — 8.4 MB over 3:30 is exactly 320 kbps, and a "320 kbps" download that comes out lower has been padded or mislabeled. Hand it a size and a bitrate and it reports how long the recording can run: a 700 MB disc at 1,411 kbps (CD audio) holds about 66 minutes. As always on this site, every calculation runs locally in your browser.