Quick path
Use the H.265 Bitrate Calculator to convert average bitrate and duration into storage, or to reverse a target file size into video bitrate.
Size formula
Add video and audio bitrate, multiply by duration in seconds, then divide by 8 to convert megabits to megabytes. For a target size, reverse the formula and subtract audio bitrate.
The calculator reports binary storage as GiB after the megabyte estimate. Container metadata, subtitles, multiple audio tracks, and muxing overhead can make the final file slightly larger than the pure bitrate math.
Target bitrate path
Start with the allowed file size, convert it to megabits, divide by duration in seconds, then subtract audio bitrate. If the result is too low for the footage, increase the size budget, reduce duration, lower resolution, or accept more compression artifacts.
Do not treat bitrate as quality
HEVC quality depends on content complexity, preset, rate-control mode, bit depth, and encoder implementation. Use the calculator for sizing and throughput, then test with representative footage.
Checks before using the result
- Use average video bitrate for file-size planning, not a short peak bitrate sample.
- Include audio bitrate when the target file includes audio.
- Run a sample encode when motion, grain, or screen detail is higher than the usual footage.
Next step
Open the H.265 Bitrate Calculator, enter the expected duration and audio bitrate, then test one representative clip before applying the number to a full batch.