Video file size calculator

How to use the video file size calculator

1. 01Pick a mode: estimate a file size, or hit a target size.
2. 02Enter the duration and bitrates, or the target size and duration.
3. 03Read the result: the estimated file size, or the bitrate you need.

How bitrate affects file size

File size scales directly with duration, and with the combined video-plus-audio bitrate: double that total bitrate at the same length and the file doubles, double the length at the same bitrate and the effect is identical. Because the relationship is a straightforward multiplication, moving any figure in the calculator shows the trade-off immediately.

Video bitrate is usually the larger of the two components in a typical export, since it carries the visual data, while audio bitrate is smaller in comparison but still counted in the total. Both are added together before the calculator converts to bytes, so raising either one raises the final file size.

A calculated figure is an estimate rather than a guaranteed exact match: most codecs use variable bitrate, so the rate moves frame to frame around an average rather than staying fixed, and the container format adds its own metadata and structural overhead on top of the raw streams. Treat the result as the number to plan around, not the byte count an exported file will land on exactly.

Hitting an upload size limit

Switch to Hit a target size mode, enter the platform's size limit and your video's duration, and the calculator solves for the video bitrate that will land at or under that limit once the audio bitrate is subtracted from the budget.

If the result comes back as too small, it means the target size cannot be met for that duration even at zero video bitrate, because the audio track alone would exceed it. Shortening the duration or raising the target size are the two ways to fix that; lowering the audio bitrate a little can also free up some headroom.

Because most encoders vary bitrate around an average rather than holding it exactly, it is worth encoding slightly below the calculated figure to leave margin, rather than treating the number as a hard ceiling the export is certain to land under.

Audio bitrate and why it matters

Audio bitrate is added on top of video bitrate as a fixed overhead, and how much of the total it makes up depends on the video bitrate, not on duration: at a low video bitrate, audio is a larger share of the total, while at a high video bitrate, the same audio bitrate is a smaller share. Duration scales the video and audio portions by the same factor, so it changes the total file size without changing that share.

The calculator defaults audio bitrate to 128 kbps, a common setting for stereo audio at a reasonable quality, but this is a default for the tool rather than a fixed requirement: change it to match whatever your own export actually uses.

When solving for a target size, a lower audio bitrate leaves more of the size budget for video, which can help hit a tight limit, though it trades away some audio quality. How much that trade-off matters depends on the content: it counts for more on a music-led edit than on a straightforward talking-head recording.

How the numbers are worked out

File size follows directly from the total bitrate and the duration: size = (video kbps + audio kbps) x 1000 / 8 x seconds, using decimal units throughout (1 MB = 1,000,000 bytes), which is how platforms usually state their upload limits.

This does not add container overhead: metadata, index tables and multiplexing usually add a small percentage on top of the raw audio and video streams, so a real exported file can come out a little larger than the calculator's figure.

Questions about the video file size calculator

How do I calculate video file size?

Add the video and audio bitrates together, convert from kilobits to bytes, and multiply by the duration in seconds: size = (video kbps + audio kbps) x 1000 / 8 x seconds. This calculator does that for you: enter a duration and both bitrates in Estimate size mode and it returns the total straight away.

What bitrate should I use for 1080p?

There is no single right answer: the bitrate a 1080p file needs depends on the codec, the frame rate, and how much motion and detail is in the footage. Rather than picking a number, use Hit a target size mode: enter your platform's size limit and the video's duration, and the calculator works out the bitrate that gets you there so you can judge the resulting quality yourself.

Why is my exported file a different size?

Most encoders use variable bitrate, so the average across the file differs slightly from a single figure entered here, and the container format adds its own metadata and structural overhead on top of the raw video and audio streams. This calculator estimates the raw streams only, so an exported file is usually a little larger than the figure it returns.

Does this include audio?

Yes. Enter your audio bitrate alongside the video bitrate and the total includes both; the default of 128 kbps is a common setting for stereo audio, but you can change it to match your own export.

Use this video file size calculator on your site

More free tools

Updated 22 September 2026 · All free tools