It's a 32 GB FAT32 USB thumb drive, and it seems to be having no trouble with my 13 GB iPhoto Library file. I thought there was a 4 GB file size limitation on this file system format?

  • 3
    Are you sure it is FAT32 and not exFAT and how did you check? What OS are you on? Is the data still readable?
    – Baarn
    Nov 30, 2012 at 14:23
  • 16
    I am going to guess you don't have a single file larger then 4GB.
    – Ramhound
    Nov 30, 2012 at 14:35
  • @informaficker - He is clearly on OS X based on the fact he is using iPhoto which only runs on OS X.
    – Ramhound
    Nov 30, 2012 at 14:36
  • 3
    @Informaficker Yes it is FAT32, I have checked with both Windows (with which I originally formatted it) and Mac. It turns out that OS X only treats the iPhoto Library as a single file in the UI, in fact it is a folder with many files inside.
    – MetaGuru
    Nov 30, 2012 at 15:02

4 Answers 4


There is a 4GB per file limit.

Copying two files, each of which is 3GB in size (6GB total) would work fine.
Copying a single 6GB file would fail.

In your case OS/X is showing iPhoto Library as a single file, but reality it is a folder with many files inside. (All smaller than 4GB).

  • 34
    I have since learned that the iPhoto Library is only treated as a single file in the file system UI, when in reality it is a folder with many files inside. You could add this to your answer and it will be complete.
    – MetaGuru
    Nov 30, 2012 at 15:03
  • 1
    Ah, the good old drawback of hiding complexity.
    – Lenar Hoyt
    Sep 1, 2013 at 17:24

A lot of the time you will find on OS X that a file is not actually a file - it is a directory. A good example of this is an application which will appear to be a single .app file but this is actually a package (directory) containing a number of files.


Yes, on FAT32 there is a file size limit, HOWEVER, it is 4gb PER FILE.

You may have a directory that is 50gb in size, however, no single file may be more then 4gb.

  • 7
    In fact, FAT disks have limits depending on FAT16/FAT32 etc. and the size of the sectors.
    – Matsemann
    Nov 30, 2012 at 17:42
  • 1
    Each partition in FAT32 is limited to 2 TB, I believe.
    – kush
    Dec 1, 2012 at 12:11

It depends on the cluster size how big the files can be. Take a look here, in the referenced support article it is described as follows:

All file systems that are used by Windows organize your hard disk based on cluster size (also known as allocation unit size). Cluster size represents the smallest amount of disk space that can be used to hold a file. When file sizes do not come out to an even multiple of the cluster size, additional space must be used to hold the file (up to the next multiple of the cluster size). On the typical hard disk partition, the average amount of space that is lost in this manner can be calculated by using the equation (cluster size)/2 * (number of files).

If no cluster size is specified when you format a partition, defaults are selected based on the size of the partition. These defaults are selected to reduce the space that is lost and to reduce the fragmentation that occurs on the partition.

But it is also the maximum file size which depends on the cluster size and also on the sector size selected, because the file size is calculated as

File size = (number of clusters) * (sectors per cluster) * (sector size)

and the sector size is usually 512 bytes, but nowadays where we have hard disks with several terabytes capacity, it can be larger (e.g. 4 KB).

While it seems that this allows larger files, the design specification of FAT32 says that a file cannot exceed 4 GB, hence

Max File size = 4 294 967 296 bytes (4 Gigabytes)

The maximum number of clusters for Fat32 is limited to 268 435 445, and a cluster must not exceed 64 KB, see here. But it is also said that you can't format Fat32 with larger clusters than 32 KB. This means that theoretically, the maximum partition size is

Max part. size = 268 435 445 * 32 768 bytes = 8 796 092 661 760 bytes (which is 8 Terabytes).

Practically, it is lower than that, because usually you don't have 32 KB clusters. For Fat32 the default cluster size varies depending on the size of the partition between 4 KB (236 MB - 8 GB partitions) and 16 KB (16 GB - 32 GB partitions).

You can influence the maximum partition size when you are formatting the partition. The larger the cluster size and/or sector size, the larger the partition can be. But the file size is always limited to 4 GB.


  • It is not dependent on the medium, you can format a memory stick or SD card with larger sectors as you can do it with your harddisk. The limitation you have depends on the system which reads the partition, for example if you're using a digital camera it might not support each sector or cluster size as your operating system on the PC does.

  • Despite the fact that Microsoft has stopped support for Fat32 partitions larger than 32 GB, you can still create and use them, if you use a free 3rd party tool to format them. Fat32 is still used by many devices and in many operating systems (not just by Windows) such as HDD recorders, cameras etc.

  • The author doesn't care about what Microsoft does or does not support they are using OS X. I have to downvote this answer for the simple fact, it doesn't help the author, because they are using OS X.
    – Ramhound
    Dec 4, 2012 at 11:46
  • Yet you talk about NTFS which OS X doesn't support without third-party drivers. OS X supports FAT32 which hasn't change in years. The same cannot be said about NTFS which has seen updates to the underline driver. You also linked to a Windows application. Make this answer relevant to the author and I might consider getting rid of my downvote.
    – Ramhound
    Dec 4, 2012 at 11:53
  • @Ramhound: But Fat32 is Windows, not OS X. So the theory about Fat32 is defined by Microsoft, not by Apple. => Think before you downvote.
    – Matt
    Dec 4, 2012 at 11:53
  • Fine. I downvoted your question because you linked to a Windows program to extend the Fat32 limits which doesn't help the author in the slightest. I very much thought about the downvote this answer does not apply to the author's question.
    – Ramhound
    Dec 4, 2012 at 11:55
  • I have removed both - the Windows program and the NTFS part.
    – Matt
    Dec 4, 2012 at 11:56

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