File Sizes

How big are files? Last week we looked at hard drives in terms of the different definitions of their size. Let’s have a look this week at the range of different sizes of files that will be stored on the drive.

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The size of computer files can be important for a number of reasons:

  • The amount of space required to store them could be relevant. Will the file(s) fit onto the chosen medium – eg internal or external hard drive, CD/DVD, USB drive? An internal hard drive, by the way, is a sealed unit that stores data and which is more-or-less permanent in the computer. It can be removed fairly easily if necessary, but in normal circumstances it remains in the computer. When the computer is started it normally looks to the internal hard drive for the programming (eg Windows or Mac operating system) to get it started. An external drive is exactly the same type of drive but it is housed in a separate box that includes the electronics to allow it to be connected to the computer by a USB cable. An external drive can be attached or removed very easily.
  • The time it takes to copy or transfer the file(s) to any of the locations mentioned above might be relevant – eg if you ask me, during the course of computer support work that I am doing for you, to copy a dozen 4gb files from one hard drive to another then that could take an hour or more. You might decide to do that copying yourself.
  • It may be that the system that will handle the files may not be able to cope – eg email attachments might be too big to be delivered.
  • There may be direct costs associated with moving/transferring files – eg the downloading costs of using a mobile phone data account, or caps on the amount of data that can be downloaded per month on a broadband account.

For all the above reasons it makes sense to have some grasp of the relative size of files so that you know whether size is an issue in any particular situation.

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Let’s start by seeing how file sizes are measured:

  • 1 byte is the room taken by a single character (a letter or a digit, for instance)
  • 1KB (kilobyte) can either mean 1000 bytes or 1024 bytes
  • 1MB (megabyte) can either mean 1,000,000 bytes or 1024 X 1024 = 1,048,576 bytes
  • 1GB (gigabyte) can mean either 1,000,000,000 bytes or 1024 X 1024 X 1024 = 1073741824 bytes

For a fuller explanation see

So, if you see a file size expressed in “KB” and the figure is less than 1000 (eg “580KB”) then you know that that file is “about half a megabyte”. Similarly, a file that is 256mb is “a quarter of a gigabyte”.

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Size and importance are not necessarily related

As things have developed over the years, I have been struck by how much variation there is now between small files and large files. The largest files are now many many times bigger than the smallest files but that doesn’t mean they are any more important. A single page Word document of much less than 1mb (your CV, for instance) is probably more important than a movie that is 4000 times as big.

Also, it’s not necessarily true that large files are less convenient than small ones. A folder containing 70mb of music files (a typical size of a complete album digitised at a reasonably high quality) doesn’t change and doesn’t need backing up more than once at most. In contrast to that, you might choose to store all your usernames and passwords in a single (password-protected) spreadsheet file. That spreadsheet file could be less than 1mb but it would be absolutely crucial to take regular backups of such a file onto media other than the hard drive it normally sits on. This file would also be a prime candidate for storing online. So, you would need to be paying far more attention to the small file than the much larger music files.

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What are some typical sizes of some popular file types?

  • Word document – anything from 5kb or less, to 1mb upwards
  • Spreadsheet – anything from 5kb or less, to 1mb upwards
  • A music track – probably about 1mb per minute of music
  • A jpg from a 3 megapixel camera at 90% quality – 504kb
  • A jpg from a 5 megapixel camera at 90% quality – 692kb
  • Video – hugely variable depending on the quality, the compression, the pixels per frame, etc. In any event, much bigger than other “data” files
  • Program files – hugely variable. It’s quite common now for a newly installed program to take up 100-200mb. Equally, you may have an indispensible little program of 5mb or less.

Next week we will look at some of the implications of dealing with files of different sizes and how we assess the size of files and the space to accommodate them.

(Last updated 07/09/2023)