A video bitrate calculator links three numbers that every encoder, editor and uploader cares about: bitrate, duration and file size. Set any two and the third is fixed. This tool works both directions — estimate the file size a given bitrate will produce, or solve for the bitrate that hits a target file size so a clip fits a disk, an email limit or an upload cap.
How it works
The whole thing rests on one identity, with total bitrate being the sum of the video and audio streams:
file size (bits) = (video bitrate + audio bitrate) × duration (seconds)
Bitrate is entered as video Mbps (×1,000,000 bps) and audio kbps (×1,000 bps). Divide the resulting bits by 8 for bytes. The tool uses decimal units throughout, so 1 MB = 1,000,000 bytes and 1 GB = 1000 MB — matching how bitrate and storage are normally quoted for video.
- Solve for size:
bytes = (video_Mbps×1e6 + audio_kbps×1e3) × seconds ÷ 8. - Solve for bitrate:
total bits = target_MB × 1e6 × 8; subtract the audio bits (audio_kbps × 1e3 × seconds); divide what remains by the duration to get the video bitrate in Mbps.
Example
An 8 Mbps video with 192 kbps audio running 10 minutes (600 s):
(8,000,000 + 192,000) × 600 ÷ 8 = 614,400,000 bytes ≈ 614 MB.
Reversing it: to fit 700 MB with 192 kbps audio over 45 minutes, the total bitrate is 700×1e6×8 ÷ 2700 ≈ 2.07 Mbps; minus audio leaves a video bitrate of about 1.88 Mbps.
| Video bitrate | Audio | Duration | File size |
|---|---|---|---|
| 8 Mbps | 192 kbps | 10 min | ~614 MB |
| 5 Mbps | 128 kbps | 30 min | ~1.15 GB |
| 2 Mbps | 128 kbps | 60 min | ~960 MB |
Everything is computed locally in your browser — nothing you enter is uploaded.