How much storage does a video recording need? The answer comes from the Video File Size Calculator: enter the recording duration and the bitrate, and you get the file size in GB and MB. This post explains the formula, a worked example and the usual bitrate guidelines.
The Formula
File size depends on two values: the bitrate (how much data is produced per second) and the duration. The basic formula is:
Size = Bitrate × Duration / 8
Dividing by 8 converts from bits to bytes, because bitrates are given in bits per second (Mbit/s) while file sizes are measured in bytes (MB, GB). One byte equals 8 bits.
Example: 60 Minutes at 10 Mbit/s
Take a 60-minute recording (3,600 seconds) at a constant bitrate of 10 Mbit/s. First convert the bitrate to bits per second: 10 Mbit/s = 10,000,000 bit/s. Then:
10,000,000 × 3,600 / 8 = 4,500,000,000 bytes = 4.5 GB
So one hour of video at 10 Mbit/s takes up around 4.5 gigabytes. If you use the calculator, you do not have to do this conversion yourself.
Bitrate Guidelines
Which bitrate is realistic? That depends on resolution and codec. As rough reference points:
1080p (Full HD): roughly 8 to 12 Mbit/s.
4K (Ultra HD): roughly 35 to 60 Mbit/s.
Higher frame rates (60 fps instead of 30 fps) or older codecs push the bitrate up further. For a first estimate, however, these ranges are enough.
Keep CBR and VBR in Mind
The formula is exact for a constant bitrate (CBR): the same amount of data is produced every second, so the result is precise. With variable bitrate (VBR) the encoder adapts the data rate to the picture content. Calm scenes need less, fast-moving scenes need more, so the actual size fluctuates around the calculated value. For planning and storage reserves, the calculation based on the average bitrate is still a reliable basis.
