Video Bitrate Calculator
A video's file size from its video and audio bitrate and length, the bitrate that fits a target file size, and the storage continuous recording needs for a number of cameras or streams over days.
Result…
How it's calculated
File size (bytes) = (video bitrate + audio bitrate) in bits a second × seconds ÷ 8 Video bitrate for a size = size in bytes × 8 ÷ seconds − audio bitrate Recording storage = streams × bitrate × hours a day × 3,600 × days ÷ 8
A bitrate says how many bits each second of video takes, so the file size is the bitrate times the length, divided by 8 to turn bits into bytes. Video and audio add together. Working backwards, a target size times 8 divided by the length gives the total bitrate the encode can use, and taking away the audio leaves the video bitrate. For security cameras and other continuous recording, each stream's bitrate times the recording time a day and the days kept gives the storage. Bitrates are always decimal: 1 kbps is 1,000 bits a second. File sizes are shown both in decimal units (MB, GB, TB) and in the binary units (MiB, GiB, TiB) some operating systems use; the data storage converter converts between them.
Your numbers, step by step
About the Video Bitrate calculator
This video bitrate calculator answers three questions video makers and security installers ask. How big will this file be? Enter the video bitrate, the audio bitrate and the length, and it gives the size in MB and GB and in the binary MiB and GiB some systems show. What bitrate fits a size limit? Enter the target size and length, and it works out the video bitrate left once the audio is taken away, handy for an upload cap or a two-pass encode. How much storage does recording take? Enter the cameras or streams, the bitrate of each, the recording hours a day and the days to keep, and it gives the total in TB and TiB along with the daily figures. Every step converts bits to bytes in the open, so you can check each number against your encoder or recorder settings.
How to use it
- Choose what to “Work out”: “File size”, “Bitrate for a size” or “Recording storage”.
- Pick whether the “Bitrate in” is kbps or Mbps, and enter the “Video bitrate” and the “Audio bitrate”.
- Enter the length in “Hours”, “Minutes” and “Seconds”, or the “Target file size” and its unit.
- For recording, enter the “Cameras or streams”, the “Bitrate per stream”, the “Recording hours a day” and the “Days to keep”.
- Read the size in decimal and binary units, or the video bitrate to set in your encoder.
Worked example
A 1 h 30 min video at 8 Mbps with 192 kbps audio runs at 8,192,000 bits a second. Over 5,400 s that is 8,192,000 × 5,400 ÷ 8 = 5,529,600,000 bytes: 5.53 GB, or 5.15 GiB, about 61.44 MB a minute. To fit 2 hours into 4 GB with 128 kbps audio, 32 × 10⁹ bits ÷ 7,200 s gives 4,444 kbps in all, leaving about 4,316 kbps for the video. Four cameras at 4 Mbps recording 24 hours a day need 43.2 GB a camera a day, 172.8 GB a day in all, and 5.184 TB (4.71 TiB) for 30 days.
Updated
Questions people ask
How do I calculate a video's file size from its bitrate?
Add the video and audio bitrates in bits a second, multiply by the length in seconds and divide by 8 to get bytes. Divide by 1,000,000,000 for GB.
What bitrate should I use to hit a file size limit?
Multiply the size limit in bytes by 8, divide by the length in seconds and take away the audio bitrate. Aim a few percent lower, because encoders rarely land exactly on the average and the container adds a little.
How much storage do security cameras need for 30 days?
Multiply the number of cameras by each one's bitrate, the recording seconds a day and the days, then divide by 8 for bytes. Cameras that record only on motion or vary their bitrate use less, so measure a real day when you can.
Why does my computer show a smaller size than this?
Some systems count in binary units, where a GiB is 1,073,741,824 bytes rather than 1,000,000,000, and still label it GB. The data storage converter converts between the two, and the download time calculator shows how long the file takes to transfer.
Is the result exact?
Only for a constant bitrate. Variable-bitrate encodes change size with the content, and the container and any subtitle or extra tracks add to it, so treat the figure as a close estimate.