Video File Size Calculator

Bitrate is measured in bits per second while file size is in bytes, so the factor of eight is unavoidable and easy to forget — an estimate that is out by exactly 8× is almost always this mistake. The other thing worth checking is whether the bitrate you need is realistic for your resolution: squeezing 1080p into a low bitrate produces blocking and smearing in fast motion, so if the required figure lands far below the typical value, you are better off dropping to 720p at a healthy bitrate than keeping 1080p at a starved one. Audio is small but not negligible: at 128 kbps it adds roughly 1 MB per minute regardless of the video.

File size in bytes = (video bitrate + audio bitrate) in kbps × 1,000 × duration in seconds ÷ 8. The division by 8 converts bits to bytes, and it is where most manual calculations go wrong.

This assumes constant bitrate. Almost all modern encoding is variable-bitrate, which targets an average, so a real file lands close but not exactly on the figure — simple footage comes in under and fast motion over. Container and metadata overhead adds roughly another 1–2%, and two-pass or constant-quality modes ignore a bitrate target entirely in favour of a quality level.

Ten minutes at 5,000 kbps video plus 128 kbps audio comes to about 366.8 MB. Working backwards, fitting the same ten minutes into 100 MB needs a video bitrate of roughly 1,270 kbps.

1. Enter the duration.
2. Choose whether you know the bitrate or the target size.
3. Enter that figure, plus your audio bitrate.
4. Compare the result against the typical bitrates for your resolution.

• Forgetting to divide by 8, giving an answer eight times too large.
• Leaving audio out of the total bitrate.
• Confusing megabits (Mb) with megabytes (MB).
• Keeping a high resolution at a bitrate too low to support it.

This calculator converts between video bitrate, duration and file size. Give it a bitrate and it returns the resulting size; give it a target size and it returns the video bitrate you need to encode at, with audio accounted for separately.

Video editors, streamers and anyone encoding video for upload, email or a platform with a size limit.

• Works in both directions — size from bitrate, or bitrate for a size.
• Separates audio from video bitrate, which most calculators fold together.
• Includes typical bitrates per resolution as a sanity check.
• Accepts duration as minutes, mm:ss or hh:mm:ss.

• Hitting a platform’s upload size limit.
• Estimating storage for a batch of recordings.
• Choosing an encoding bitrate for a target quality.
• Checking whether a file will fit an email attachment limit.