SPACEBACK · PRACTICAL COMPRESSION
Plan a smaller video before you export
Will 720p give you the file size you need? This free calculator uses the same bitrate model as SpaceBack’s video presets. No sign-in or file selection is needed. It runs in your browser.
How to use the estimate
Find size, duration and dimensions in your file’s information panel. Enter the size in MB: 1 GB is 1,000 MB in this calculator. For a portrait video, keep width and height in their original order. The calculator fits the picture inside the selected resolution without enlarging it.
If you are trying to meet an attachment limit, leave a margin below it and check the actual saved file. SpaceBack does not currently provide a guaranteed target-size export. Try a short representative clip before processing a large batch.
What the numbers mean
File size is approximately total bitrate multiplied by duration, divided by eight. This model derives an average rate from your original size, applies the selected preset and allows 2.5% for container overhead. With audio selected it budgets 160 kbps; the real compressor may use the detected audio rate instead.
Resolution is only one part of the result. Grain, rapid movement, detailed foliage, encoder behavior and the source codec affect visible quality and final bytes. A 4K label cannot restore detail missing from an original. A heavily compressed source can get larger if encoded again.
This calculator does not check device codec support, HDR, available storage or whether a file is valid. It is an estimate, not a demonstration of achieved savings.