What this Video File Size Calculator does
The Video File Size Calculator estimates how much storage a video may use from three values: its running time, video bitrate, and audio bitrate. It adds the audio and video bitrates, converts the total data rate into bytes, and reports an estimated size in decimal gigabytes (GB). This gives you a practical planning figure when you are preparing a streaming upload, saving a home viewing copy, or checking whether a device has enough free storage.
The estimate assumes that the selected bitrates remain constant for the entire video. Actual files also contain container metadata, subtitles, chapter information, and other stream data. Variable bitrate encoding can also make the average rate differ from a target or peak rate. For those reasons, treat the result as an informed estimate rather than an exact prediction of a finished file.
How to use the Video File Size Calculator
Enter the duration in minutes, the video bitrate in megabits per second (Mbps), and the audio bitrate in kilobits per second (kbps). Use values that describe the version you plan to store or deliver. If your editor or encoder shows a combined bitrate, separate video and audio values are needed for this calculator. If audio is absent, enter zero for its bitrate.
- Duration: Use the full running time of the video. A 90-second clip is 1.5 minutes.
- Video bitrate: Enter the video stream's average or target bitrate in Mbps.
- Audio bitrate: Enter the audio stream's bitrate in kbps, such as 192 kbps.
For example, consider a 10-minute home movie with video at 8 Mbps and audio at 192 kbps. The combined rate is 8 + 192 / 1000, or 8.192 Mbps. The calculator estimates (10 × 60 × 8.192 × 1,000,000) / 8,000,000,000, which equals 0.61 GB after rounding to two decimal places. The conversion uses eight bits per byte and one billion bytes per decimal gigabyte.
How the Video File Size Calculator formula works
The formula first changes minutes into seconds by multiplying duration by 60. It converts audio bitrate from kbps to Mbps by dividing by 1,000, then adds that value to the video bitrate. The combined Mbps figure is multiplied by one million to express bits per second. Multiplying by the video's seconds gives total bits. Dividing by eight converts bits to bytes, and dividing by one billion converts bytes to decimal GB.
In compact form, the calculation is: (duration in minutes × 60 × (video Mbps + audio kbps / 1,000) × 1,000,000) / 8,000,000,000. Each input has a distinct role, so changing the runtime or either bitrate changes the estimate proportionally. For example, doubling duration while keeping both bitrates fixed doubles the predicted size.
Some operating systems and storage tools use binary units, where a gibibyte (GiB) equals 1,073,741,824 bytes. The calculator reports decimal GB, where one GB equals 1,000,000,000 bytes. A displayed size in GiB will therefore be numerically lower for the same file. This is a difference in unit convention, not a change to the underlying video.
Use cases for the Video File Size Calculator
A size estimate is useful at several points in a streaming and home viewing workflow. Before recording or exporting, it can help you compare a few plausible bitrate settings and understand the storage tradeoff. Before copying a collection to a laptop, media server, or external drive, it can provide a rough total for an individual title. For multiple videos, calculate each one and add the results, or estimate a group with a representative duration and bitrate when the files are similar.
It can also help with upload planning. A larger encoded file takes longer to transfer on the same connection, though transfer time depends on the available upload speed and network conditions. This calculator does not estimate that time. It only estimates the data volume, which is one of the inputs you may need when planning a transfer or deciding how much free storage to reserve.
When comparing two exports of the same program, keep duration and audio bitrate fixed while changing video bitrate. The resulting size difference shows the approximate storage cost of the bitrate change under the constant-rate assumption. It does not determine which version looks better. Perceived quality depends on the codec, resolution, frame rate, scene complexity, and encoding choices as well as bitrate.
Other factors to consider when calculating video size
The estimate covers the selected audio and video streams. A finished media file may also include subtitles, multiple audio languages, cover art, indexes, and container overhead. These additions are often modest for a single short video, but they matter when you need a close storage budget across a large library. Leave extra space for the final file and any temporary export files created by your software.
Bitrate behavior is another source of variation. Constant bitrate aims to keep the data rate near a set value. Variable bitrate encoding allocates more data to complex scenes and less to simple scenes, so the actual average determines the final file size. If you enter a maximum bitrate instead of an average or target, the estimate may overstate typical size. Check your encoder's output statistics when available, then use the average rates for a closer calculation.
Codec and resolution choices influence how much bitrate is needed for a particular viewing result, but they do not change this formula directly. A newer codec may achieve similar visual quality at a different bitrate, while high motion, grain, or detailed scenes can require more data. This tool does not evaluate quality or recommend an encoding setting. Use test exports and playback on the intended screen to assess those questions.
FAQ
Does the result show decimal GB or binary GiB?
It shows decimal gigabytes. One GB is treated as one billion bytes. A device that reports binary gibibytes uses a larger byte count per displayed unit, so its numerical figure for the same file will be smaller.
Can I use a combined audio and video bitrate?
The inputs are separate so the calculator can convert their units correctly. If you have a combined bitrate already expressed in Mbps, you can use it as the video bitrate and set audio to zero. The total-rate arithmetic will then use that combined value.
Why is my exported file larger than the estimate?
The actual average bitrate may be higher than the values entered, particularly with variable bitrate encoding. The container, extra audio tracks, subtitles, metadata, and other streams can add data too. Compare the export's reported average rates and included tracks with your inputs.
Does this calculator predict video quality?
No. It estimates storage from duration and bitrate only. Quality depends on encoding settings and content, including codec, resolution, frame rate, and scene complexity. A size estimate cannot replace an export test or direct viewing check.
How should I estimate a playlist or collection?
For the most useful estimate, calculate each video's size using its own runtime and bitrates, then add the results. If all videos have similar settings, multiplying a representative estimate by the number of videos can provide a quick approximation, with extra room reserved for variation and file overhead.