Video File Size Calculator

How the file size is calculated

The file size is the bitrate (the amount of data used per second) multiplied by the length of the video.

• Total bitrate = video bitrate + audio bitrate
• File size (bytes) = total bitrate (bit/s) × length (seconds) ÷ 8

The division by 8 is there because the bitrate is in bits and the file size is in bytes (1 byte = 8 bits).

Example

A video with a video bitrate of 8 Mbps, an audio bitrate of 192 kbps and a length of 1 hour:

1. Total bitrate = 8,000,000 + 192,000 = 8,192,000 bit/s
2. Length = 3,600 seconds
3. File size = 8,192,000 × 3,600 ÷ 8 = 3,686,400,000 bytes

3,686,400,000 bytes is 3.6864 GB in steps of 1,000, and about 3.433 GiB in steps of 1,024.

Assumptions and notes

• k and M in bitrates are steps of 1,000. 1 Mbps = 1,000 kbps = 1,000,000 bit/s.
• For a video with a variable bitrate, enter the average bitrate. The real file size depends on the content of the video.
• The overhead of the container (the file format, such as MP4, that holds the video and audio together) is not included. A real file can be a few percent larger than the calculation.
• If you leave the audio bitrate empty, it is treated as 0 (a file with video only).
• The length can be from 0 seconds to 999 hours 59 minutes 59 seconds. The video bitrate must be greater than 0 and can have decimals.
• To see how size units such as GB and GiB differ, use the Data Size Converter.

When you want to know how much video fits

To find how long a video fits in a given amount of space, use the formula the other way around.

• Recording time (seconds) = size (bytes) × 8 ÷ total bitrate (bit/s)

For example, a total of 8.192 Mbps saved to 128 GB (128,000,000,000 bytes) gives 128,000,000,000 × 8 ÷ 8,192,000 = 125,000 seconds (about 34 hours 43 minutes). Allow some margin for overhead. The Video Bitrate Calculator does this calculation, and also the bitrate from a size and a duration.

Source

The formula size = bitrate × time ÷ 8 follows Wikipedia, "Bit rate": https://en.wikipedia.org/wiki/Bit_rate (read on November 1, 2026; only the first part of that long page could be read word for word, and it gives the file transfer rate as the file size in bytes divided by the time in seconds and multiplied by eight). It is an explanatory article, not a standard.

Frequently asked questions

What is a bitrate?

The amount of data used per second. A higher number makes it easier to keep the picture and sound quality, but the file gets bigger.

Do I need to enter both video and audio?

A video without sound can be calculated from the video alone. If there is sound, enter the audio bitrate too to get closer to the real size.

Why does the real file size differ from the calculation?

Because of the average of a variable bitrate, the overhead of the container, subtitles, metadata and so on. Use it as a guide.