Video File Size Estimator
Work out how big an export will be before you render it.
- Runs entirely in your browser
- Nothing is uploaded
- Works offline once loaded
How the estimate works
File size comes almost entirely from bitrate multiplied by duration. The formula is bitrate in bits per second, times duration in seconds, divided by eight to convert to bytes.
The container — the MP4 or MOV wrapper — adds roughly two percent for metadata and indexing. The estimate shows that separately so you can see both the raw stream size and the realistic figure.
Typical bitrates
- 1080p social upload — 8 to 12 Mbps
- 4K social upload — 35 to 45 Mbps
- 720p, bandwidth conscious — 4 to 6 Mbps
- Audio, stereo AAC — 128 to 192 kbps
When your export is too large
If your file is landing above an upload cap, lowering the bitrate is almost always a better trade than lowering the resolution. A 1080p video at a reduced bitrate generally looks better than a 720p video at a high one, because you keep the detail in static areas.
The exception is fast motion. Heavy movement genuinely needs the bits, and a low bitrate at high resolution will fall apart into blocking. For action footage, dropping resolution is the better call.
Audio is almost never the problem
Run the numbers and you will see that audio is a rounding error next to video. Thirty seconds of 128 kbps stereo is under half a megabyte. If your file is too big, the video stream is why.
Frequently asked questions
Why does my real export differ from the estimate?
Most encoders use variable bitrate, spending more on complex scenes and less on simple ones. Your stated bitrate is a target average, so the final size lands near the estimate rather than exactly on it.
What about constant quality encoding?
Modes such as CRF in H.264 target a visual quality level rather than a bitrate, so the final size depends entirely on content and cannot be predicted in advance. This estimator applies to bitrate-targeted exports.
Every SnapView tool runs inside your browser. Files you open here are read by your own device and are never uploaded, stored or transmitted anywhere. You can disconnect from the internet after this page loads and the tools will still work — which is the simplest way to verify that claim for yourself.