The difference with and without -h should only be the human readable units, right?

Well apparently no...

$ du -s .
74216696    .
$ du -hs .
 35G    .

Or maybe I'm mistaken and the result of du -s . isn't in KB?

  • 3
    Try using du --block-size=1024 -s .. Maybe your BLOCK_SIZE is set to 512
    – Echoes_86
    Commented Jan 4, 2017 at 18:04
  • 6
    From the (OSX) manual page: "If BLOCKSIZE is not set, and the -k option is not specified, the block counts will be displayed in 512-byte blocks" Commented Jan 4, 2017 at 18:06
  • Which is not super-helpful if the filesystem is actually in 4096-byte blocks.
    – DopeGhoti
    Commented Jan 4, 2017 at 18:06
  • So there is no way to have the size in bytes? I thought -h was just dividing by 1024 and adding some units
    – Creak
    Commented Jan 4, 2017 at 21:13
  • 2
    echo "74216696*512" | bc outputs , 37998948352. And yes, -h converts to human readable form by dividing over and over by 1024. What I got was 35.3887 , which is awfully close to what du reports. As for size in bytes, just use --block-size=1. On Linux, there's -b option for that, but I'm not familiar with OS X du Commented Jan 5, 2017 at 3:01

2 Answers 2


du without an output format specifier gives disk usage in blocks of 512 bytes, not kilobytes. You can use the option -k to display in kilobytes instead. On OS X (or macOS, or MacOS, or Macos; whichever you like), you can customize the default unit by setting the environment variable BLOCKSIZE (this affects other commands as well).

  • 1
    Didn't know that... What's the interest in having the number of blocks? I have never seen one person using blocks when talking about sizes on disk...
    – Creak
    Commented Jan 4, 2017 at 21:15
  • 2
    Blocks are the atomic unit of filesystems. Any file will consume a whole-number of blocks on the disk. A block may only be partially filled with actual data, but the entire block is allocated to the file. Most folks' day-to-day usage doesn't care about blocks other than in a percentage-used-versus-free sense. But low level utilities (e. g. fdisk, df, and du) work in blocks unless directed otherwise because that is the unit by which they count internally.
    – DopeGhoti
    Commented Jan 4, 2017 at 23:17
  • 1
    @Creak Actually, that part of the answer was wrong. The unit is not the block size of the filesystem. For the purposes of classic Unix commands such as du, “block” means 512 bytes. See file block size - difference between stat and ls, Difference between block size and cluster size Commented Jan 4, 2017 at 23:44
  • 3
    "Any file will consume a whole number of blocks on the disk." Well, generally yes—unless your filesystem uses tail packing. But yes, blocks are the basic unit of the filesystem (although the actual block size doesn't necessarily align to the block size used by du.) :)
    – Wildcard
    Commented Jan 4, 2017 at 23:58

The problem is that du returns the size in number of blocks of 512 bytes.

In order to have the size in KB, you can use the -k option that use 1024-byte blocks instead:

$ du -ks .                            
43351596    .
$ du -khs .
 41G    .

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