FREE VIDEO FILE SIZE CALCULATOR
Video File Size
Calculator
Estimate file size from bitrate and duration, or work backward from a target MB.
Instant math. No upload. No signup.
✓ File size estimate✓ Target bitrate✓ MB + MiB
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Video details
Use the average bitrates you expect the finished file to have.
Video presets
01
Target details
Find a practical starting video bitrate that leaves room for audio and container overhead.
THE MATH, WITHOUT THE MYSTERY.
How video file size is calculated.
For constant or average bitrate, file size is mostly duration multiplied by the combined video and audio bitrate. Real encoded files can differ because containers add overhead and variable-bitrate encoders spend more bits on complex scenes.
File size (MB) ≈ (video kbps + audio kbps) × seconds ÷ 8000Video kbps ≈ target MB × 8000 ÷ seconds − audio kbpsSmallerKit's target-bitrate mode can reserve 3–5% headroom so the estimate is less likely to overshoot a hard size limit.
These are mathematical estimates using decimal MB. Actual encoded files can vary.
WHY THIS HELPS.
Plan before you compress.
If a platform gives you a hard upload limit, the target-size calculator tells you the bitrate budget available for the whole video. That gives you a practical starting point before encoding.
For example, a 25 MB limit over five minutes allows far less bitrate than the same 25 MB over one minute. Duration is the biggest reason one universal compression setting cannot work for every file.
GOOD QUESTIONS.File-size math,
File-size math,
made practical.
What the calculator can and cannot predict.
Will the real file size exactly match the calculator?+
No. The estimate is strongest when you know the average bitrate. Container overhead, variable bitrate, codec behavior and metadata can make the actual result a little different.
What bitrate should I use for a 25 MB video?+
It depends on duration and audio bitrate. Switch to “Fit a target size,” enter 25 MB and your duration, and SmallerKit calculates the remaining video bitrate budget.
Should I use MB or MiB for upload limits?+
Use MB unless the service explicitly says MiB. Most web upload limits are described using decimal megabytes.
Does the calculator upload anything?+
No file is selected or uploaded. The calculations happen locally in JavaScript. SmallerKit's cookie-free analytics records ordinary pageviews and product-event names, not the numbers you enter into the calculator.