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Video File Size & Bitrate Calculator
Enter resolution, frame rate and duration, then either a target bitrate or a target file size — this calculator computes the other value and shows the result in MB and GB against common upload limits like Discord, email and Instagram Reels.
How the calculation works
Video files are, at their core, a data rate sustained over time: file size in bits equals total bitrate (video plus audio, in bits per second) multiplied by duration in seconds. This tool runs that formula both directions — give it a bitrate and it computes size, or give it a target size and it works backward to the bitrate you'd need to hit it.
What this can't do
This is a container-level estimate. It doesn't account for variable bitrate encoding swings, container overhead, multiple audio tracks, or how a specific encoder (x264, x265, hardware encoders) actually spends its bitrate budget on a specific clip. Treat the output as a solid planning number, not the exact byte count your export will produce.
Frequently asked questions
Why does my exported file not match the calculated size exactly?
Most modern encoders use variable bitrate (VBR) rather than a perfectly constant rate, so busier scenes get more bits and static scenes get fewer. The bitrate you set is usually a target average, not a hard ceiling, so real output typically lands close to — but not exactly at — the calculated size.
Should I calculate from bitrate or from target size?
If you have a quality target in mind (e.g. "8 Mbps looks good for this content"), start from bitrate. If you have a hard size limit to hit (a 25MB upload cap, a 4GB Reels limit), start from target size and let the tool tell you the bitrate ceiling you need to stay under.
Is audio bitrate really worth accounting for separately?
Yes — at typical video bitrates it's a small slice, but at low target bitrates (short clips near a strict size cap) 128–320 kbps of audio can be 5–15% of your whole budget, which matters when you're right at the edge of a limit.
Why are the platform limits shown as MB, not exact rules?
Upload limits change over time and vary by account tier (e.g. Discord Nitro vs. free), so these are shown as commonly cited reference points to sanity-check against, not a guarantee of what any platform will accept today.