Video bitrate calculator
Enter the file size you want, how long the video runs and the audio bitrate. The calculator gives the video bitrate to set in your encoder so the file lands on that size.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Enter the size the file must fit, such as 4 GB or 700 MiB, and pick the unit.
- Enter the running time in hours, minutes and seconds.
- Enter the audio bitrate in kbps (128, 192, 320 …).
- Set the video bitrate shown in kbps or Mbps as the average bitrate in your encoder.
total bitrate = size in bytes × 8 ÷ duration in seconds
video bitrate = total bitrate − audio bitrate
The calculator divides by 1,000 to show kilobits per second (kbps), as encoders expect, and by 1,000,000 for Mbps.
Worked example
A 1 h 30 min film must fit 4 GB with 128 kbps audio.
- 4 GB = 4,000,000,000 bytes = 32,000,000,000 bits.
- 1 h 30 min = 5,400 s, so the total bitrate is 32,000,000,000 ÷ 5,400 = 5,925,926 bit/s = 5,926 kbps.
- Video: 5,926 − 128 = 5,798 kbps, about 5.8 Mbps.
For 700 MiB and 192 kbps audio over the same time: 700 × 1,048,576 × 8 ÷ 5,400 = 1,087 kbps in all, so about 895 kbps of video.
Tips
- Leave 2–5 % spare for the container and for encoder drift when the size limit is hard, such as an upload cap.
- If the result is very low for the resolution, the picture will suffer: lower the resolution or allow a bigger file.
- For the opposite question, how big a file a bitrate makes, use the video file size calculator.
Frequently asked questions
How do I calculate video bitrate from file size?
Turn the size into bits (bytes × 8) and divide by the running time in seconds. That is the total bitrate; subtract the audio bitrate to get the video bitrate. A 4 GB file of 1 h 30 min is 32,000,000,000 bits ÷ 5,400 s = 5,926 kbps in all, or 5,798 kbps of video with 128 kbps audio.
What is the difference between MB and MiB here?
MB and GB are decimal: 1 MB = 1,000,000 bytes and 1 GB = 1,000,000,000 bytes. MiB and GiB are binary: 1 MiB = 1,048,576 bytes and 1 GiB = 1,073,741,824 bytes. Windows shows binary sizes but labels them GB, so a disc or card limit is often easier to hit with GiB.
Will the encoded file be exactly this size?
Close, but usually not to the byte. The container (MP4, MKV) adds a little overhead, and encoders in constant-quality or single-pass modes drift from the target. Two-pass encoding with this average bitrate gets nearest. Leave a few percent spare if the limit is strict.
Why is the audio bitrate subtracted?
The file holds both tracks. The total bitrate is shared between them, so the video gets what is left after the audio. Several audio tracks or subtitles take their share too: add their bitrates into the audio field.