Manually calculate the bitrate of a video from its file size and length. This can be done for both Megabits per second and Kilobits per second.
Bitrate is the number of bits processed per specified unit of time. The more per time means more data is being sent. For video, this means the higher the bitrate the more detail being processed during the time frame.
Bytes to Bits
Filesize is stated in Bytes whilst video is Bits. There are 8 Megabits to a Megabyte so to convert the video size into Bits you will have to multiply the size in Megabytes by 8.
You now have Megabits, to get the Megabits per second divide by the length of the video in seconds.
(size * 8) / length
This will give the bitrate reading as Megabits per second (Mbps).
As Kilobits per second
If you want the bitrate to be in Kilobits per second (Kbps) multiple this value by 1000:
((size * 8) / length) * 1000
A short clip that is 12.5 Megabytes in size and 18 seconds long:
(12.5 * 8) / 18
This equals 5.55, meaning 5.55 megabits per second. To get this as kilobits per second multiple it by 1000.
Therefore the clip is 5,555.55kbps.