I have noticed this mainly with torrents, but also with other things.

For example, if I download a ~700MB movie, it'll download and take up ~760MB on my mac. The exact same torrent will take up the ~700MB listed on the download page on my Nexus 7, or on a Windows 7 desktop.

I've also seen this space increase with photos from a digital camera (JPG format), movie files from Final Cut Pro, downloaded files like images, word documents, PDFs etc. Mostly with small files the difference is negligible, usually amounting to a few kB. However, when the files are bigger, the difference is harder to ignore.

Does anybody know why this happens? Is it because of the Mac OS X filesystem as opposed to NTFS and FAT on Windows or YAFFS2 and vFAT on Android?

Or does Mac store files in a different way?

I would prefer a canonical answer if possible.

  • Yes Raghav, i think it's because of File System structure only, i have 8 GB Pen Drive with FAT32 System, and i can't copy 5.5 GB's file which is in Linux System, it gives error as no more space in pen drive, however pen drive is just empty, all 8GB is available.
    – Lucifer
    Oct 27, 2012 at 9:28
  • 3
    @Lucifer That's because FAT32 has a maximum file size of 4GB minus 1 byte. However, I'm not asking about the maximum file size. I'm asking why it is like this, and I think it's because of the file system structure as well. Oct 27, 2012 at 9:30
  • 1
    that's what i am saying, it's because of File Structure of the Operating System.
    – Lucifer
    Oct 27, 2012 at 9:31
  • In windows, when you right click and bring up file properties, you get 2 numbers, "size" and "size on disk". Can you give us those full numbers. And the equivilant full number(s) for mac OS?
    – weston
    Oct 27, 2012 at 9:36
  • Closely related, but not exactly the same issue: How much storage am I using?
    – slhck
    Oct 27, 2012 at 10:01

3 Answers 3


Are you sure that you are always using the same unit ?

Some programs count bytes by multiples of 1000, others by multiples of 1024. This way, a file of one billion bytes will be 1000 000 000 bytes, or 1000 MB (megabyte), but only 954 MiB (mebibyte).

See http://en.wikipedia.org/wiki/Mebibyte


A few years ago, Mac OS X Snow Leopard changed the size of a MB to the standard that mega is 1000000 and not the historical 1048576 [1].

So if you compare the actual number of bytes used by the files, it should be the same.

[1] http://reviews.cnet.com/8301-13727_7-10330509-263.html

  • ...and I guess they did it so people would finally stop complaining "My new 3 TB drive only has 2.7 TB! I'm being robbed!" Oct 28, 2012 at 7:38
  • That, and using 1000 bytes == 1 KB is correct according to the standards. Nov 20, 2012 at 15:59
  • 1
    Of course, everyone knows the "standards" weren't designed out of good heart to get the binary prefixes SI-compatible, but because of disk drive industry lobbying. I mean, "kibibyte"? Come on. The metric system shouldn't even apply here, for many reasons. But hey, it's the standard...
    – Thomas
    Feb 23, 2013 at 13:27
  • @Thomas It had almost nothing to do with disk industry lobbying but actual inconsistencies in usage. For example, "gigabit Ethernet", has a line speed of 1 billion bits per second. So should that be ".93 gigabit Ethernet"? Or are you going to blame Ethernet industry lobbying? Nov 6, 2014 at 19:24

It is because

Microsoft defines 1GB as 1024 MB. Apple, on the other hand, defines 1GB as 1000 MB.

See here, here

  • 1
    How is this better than other answers?
    – Toto
    Mar 27, 2018 at 11:28
  • 1
    It is more precise Mar 28, 2018 at 6:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.