How to hit a target video file size
Upload caps and storage budgets set a size you cannot exceed. Here is how to work backward from that limit to the bitrate your export should use.
Start from the limit, not the bitrate
When a platform or storage budget caps how large a file can be, the cleanest workflow is to treat the size as fixed and solve for the bitrate that fits it. Set the Solve for menu to Bitrate, type the size cap in MB and the clip length in seconds, and the calculator returns the highest average bitrate that stays under the ceiling. Encoding at or just below that number is what keeps a video within an email attachment limit or a chat platform's per-file cap.
Leave headroom for overhead and audio
The formula gives the size of the media stream itself, but a finished file also carries a container, metadata and often a separate audio track. Those extras are small yet real, so aiming for the exact cap can push the final file just over the edge. A safe habit is to target roughly ninety to ninety five percent of the limit, and to add the audio bitrate to the video bitrate before you calculate rather than treating audio as free.
Constant versus variable bitrate
The calculation assumes a constant average bitrate. Real encoders often use variable bitrate, spending more bits on fast, detailed motion and fewer on still scenes. Over a whole clip the average lands near your target, but the peak can be higher, which matters when a strict per-file limit is involved. If you must stay under a hard cap, encode with a capped or two-pass average bitrate mode so the encoder holds the mean you calculated.
Trading quality for size sensibly
Once you know the bitrate a size cap allows, you can judge whether the quality will hold up. A short clip has generous bits per second to spend and can look sharp, while squeezing a long recording under the same cap forces a low bitrate and visible compression. If the solved bitrate looks too low, the real fix is usually to shorten the clip, drop the resolution, or split it into parts rather than pushing the encoder past what the cap allows.