How to Calculate the Size of a Video

Calculating the size of a video can be complicated. To send one on WhatsApp or Telegram, for example, you cannot exceed the limit of 100MB or 2GB, depending on which app you use. To understand how to calculate the size of a video and estimate it in advance, for example in post-production or editing or simple export or conversion, you need to start from a basic consideration:

the size of the video will not be equal to the sum of the individual images that compose it

This might seem strange, but it depends on the video format used. Generally, the videos adopt a so-called differential encoding and can compress the format using various “technical tricks”. This means that the calculation of the size may not be as obvious as it may be in other file formats. To this I would add, in the second instance, the fact that:

the size of a video depends not only on the resolution but also on the bitrate of the video itself

Technically you could have a 4K video with a lower resolution or inadequately exploited. This too must be considered if you want to learn how to correctly estimate this size. The size of a video can also be calculated, in this preliminary phase at least, as the sum of the size of the video and the size of the audio of the file itself. Many common video formats can be .MOV and .AVI, and each of them will have format specifications which, however, we will avoid going into further at this stage.

Calculation formula

The formula to calculate the size of a video is given in general by this formula, which is a multiplication of 3 factors that contribute to the size itself:

video file size = bitrate x duration x compression ratio

Bitrate

the bitrate is given by the following formula:

Bitrate = frame size (frame) x frame rate

Duration

The duration of a video is expressed for convenience in seconds. In the previous formula, for which a video of 1 hour and a half will obviously be equal to 90 minutes = 540 seconds.

Compression ratio

This ratio is a ratio of two integers, where 1: 1 indicates a lack of compression and 1: 200 is a higher compression level.

Example of calculating the size of a video

In the following table, we find some examples of video duration in relation to the occupation of a GB of space, just for reference.

Resolution Bitrate 1 minute Minutes / GB
4K
20 Mbps 84MB 12 minutes
1080p
5 Mbps 20MB 50 minutes
720p
1 Mbps 5MB 3.5 hours
480p
500 Kbps 2MB Eight hours

How to use this table: just take it as an indicative reference and you will immediately have an estimate of how much each video made with the corresponding resolution in standard or medium coding conditions will occupy. A 4K video of 60 minutes, therefore, will occupy  84 * 60 = 5040 MB, multiplying the minutes by the actual duration (60 in this case).

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