I usually have trouble intuitively comprehending how much I can really store when someone says that a certain product from so-and-so company will allow you to store 80 GB worth of songs, while another gives you 160 GB, and so forth. The numbers standing alone by themselves just seem so abstract, and to me they seem like they can only be measured relative to each other!

I was just wondering if there are any "rules of thumbs" for different files such as text file, mp3 file, small Word file, video, e-mail, etc. I understand that even within a certain type, they are all different, but is there a general, common-sense kind of number that is usually used to describe them?

Text file - ?
mp3 file - ?
small Word file - ?

Or at least, is there a quick way to approximate it for each specific case you encounter?


2 Answers 2

  • For text files, it depends on the encoding. If you use ASCII, then it will be 1 byte/char. If you use UTF-8, then it will depend on the particular characters, varying from 1 to 4 bytes/char. But this mainly applies to East Asian languages with lots of characters. If you convert an ASCII (only Latin alphabet) file to UTF-8, the difference in file size should be minimal.

  • For MP3 files, it really depends on the encoding. If you have a high bitrate MP3, it will take a lot more space than something low bitrate. You can go on the rough estimate of 5 MB/file though.

  • Word files depend on the format .doc vs .docx. At a rough estimation, Word is probably 10 KB/page, except for when pictures are pasted into them (difficult to predict the size).

Also remember the difference between SI decimal prefixes and IEC binary prefixes: 1 kilobyte (KB) = 10^3 = 1000 bytes for SI, 1 kibibyte (KiB) = 2^10 = 1024 bytes. Although they shouldn't, most hard drive manufacturers mix this up in their favor.

  • Thanks. I'm just curious, but why are there different character encodings out there? Why can't just stick with a standard? Oct 29, 2011 at 20:48
  • 1
    @JacobHayden: It's because not everyone out there speaks English. . .
    – surfasb
    Oct 30, 2011 at 9:29
  • @JacobHayden: UTF-8 is the modern standard. ASCII is a legacy left over from when computing was mainly limited to English-speaking countries, so to save space (which was scarce back then), only the Latin alphabet, Arabic numerals, and some punctuation was available.
    – Samir Unni
    Oct 30, 2011 at 21:21

The tricky part here is that all of the answers depend on how much data there is in the file, i.e. twice as many pages of text in the text file will double the file size.

  • For the text files i have lying around it is about 2kB per page.
  • mp3 file depends on both length and amount of compression. For a 128 kbps file (like the ones floating around on P2P networks) it is about 1 MB per minute, so a 3 min song is 3MB. For higher quality stuff like what you buy from iTunes or Amazon (which is 256 kbps) it is 2 MB per minute so the same 3 min song is 6 MB.
  • The Word file depends greatly on what you put in it. A one page .doc file with normal formatting (i.e. paragraphs and headings and stuff) is about 26kB plus 4 kB per page, while for a .docx the size is about 10 kB plus 3kB per page. If you add pictures or such the size will balloon, of course.

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