How to use it
- Choose Calculate: File size from the bitrates or Video bitrate for a target size.
- For a size, type the Video bitrate (Mbit/s). For a target, type the Target file size and choose the Size unit.
- Type the Audio bitrate (kbit/s) and the Duration (minutes).
- Read the File size (MB, decimal) and the File size (MiB, binary), or the Video bitrate needed (Mbit/s).
File size from bitrate and time
A file holds the bits of the video and of the sound for the whole length. The bitrate is the number of bits per second, so the total bits are (video bit/s + audio bit/s) × seconds. The Wikipedia article on bit rate gives the units: 1 kbit/s is 1000 bit/s and 1 Mbit/s is 1000 kbit/s. A byte is 8 bits, so the size in bytes is the total bits divided by 8.
The estimate counts the video and audio bits only. Subtitles, chapters or any other data in the file are not included.
total bit/s = video bit/s + audio bit/s
bytes = total bit/s × seconds ÷ 8
MB (decimal) = bytes ÷ 1,000,000; MiB (binary) = bytes ÷ 1,048,576MB and MiB: two sizes of a megabyte
The Wikipedia article on the megabyte says the word is used for both 1000 and 1024 bytes. The IEC standards give the decimal meaning to megabyte (1,000,000 bytes) and the binary one to mebibyte, MiB (1,048,576 bytes). This tool shows both. Data rates such as Mbit/s always use decimal prefixes (Wikipedia: Data-rate units), so the bitrates are in decimal units.
The gap matters for a file. The Wikipedia article on the gigabyte gives an example: Microsoft Windows shows a 400 GB drive as 372 GB, which is 372 GiB, because the system counts in binary units under the decimal label. A file that your system names in GB may therefore be in binary units.
Bitrate for a target size
To fit a target size, turn the formula round. The video bitrate is the target in bytes × 8 ÷ seconds, minus the audio bitrate. Choose the unit that matches the limit you have: a limit of 700 MiB is 4.9 % more bytes than 700 MB.
video bit/s = target bytes × 8 ÷ seconds − audio bit/sExample: a 90-minute video at 5 Mbit/s
The video has 5 Mbit/s of video and 128 kbit/s of audio, so the total is 5.13 Mbit/s. Over 5,400 seconds that is 27,691,200,000 bits, or 3,461,400,000 bytes: 3,461.4 MB in decimal units, or 3,301.0 MiB in binary units.
For a 700 MB limit over 74 minutes with the same audio, the video can have 1.13 Mbit/s.
| Measure | Value |
|---|---|
| Total bitrate | 5.13 Mbit/s |
| File size, decimal | 3,461.4 MB |
| File size, binary | 3,301.0 MiB |
| Video bitrate for 700 MB in 74 minutes | 1.13 Mbit/s |
Frequently asked questions
Why is my file bigger than the estimate?
The calculator counts only the video and audio bits. Subtitles, chapters, metadata and other tracks add data on top, so the real file can differ from the estimate.
What is the difference between Mbit/s and MB/s?
Mbit/s counts megabits, and a byte is 8 bits, so 8 Mbit/s is 1 MB/s. The Wikipedia article on data-rate units gives the same relation: 1 Mbps is 0.125 MB/s.
Which unit should I choose, MB or MiB?
They differ by about 4.9 %. Use the unit of the limit you are given. The result shows both sizes, so you can compare the file with either limit.
Does the audio bitrate change the size much?
It adds to the bits of every second, so it counts in the estimate. At 128 kbit/s it is about 2.5 % of a 5 Mbit/s video, and a larger audio bitrate takes a larger share.
Does the tool show the quality of the video?
No. It gives the size for a bitrate. The bitrate is a setting of the encoder, and the calculator does not measure the picture or the sound.
Is my video uploaded when I calculate?
No. The tool does not read any file. It works from the numbers you type, in your browser, and nothing is sent to us.
Sources
Figures and text last checked on Tuesday, November 10, 2026.