How to use it
The calculator gives a practical starting bitrate for a target file size. For example, the default values represent a 1 hour 30 minute video, 128 kbps audio and a target size of 698 MB.
Fine-tuning an encode
If your first encode is slightly over or under the required size, you can refine the bitrate using the size actually achieved:
old bitrate ÷ achieved size × required size
For example, if an encode at 949 kbps produces a 619 MB video and you need 614 MB:
949 ÷ 619 × 614 ≈ 941 kbps
Re-encoding at roughly 941 kbps should bring the result closer to the required size.
A legacy tool that still has a use
This calculator dates from the era when fitting video to fixed-size media was common, but the same basic bitrate budgeting remains useful whenever you need to work toward a known file-size limit.