I recently ran df -h on my Mac using Terminal. I was surprised to find that it shows my internal volume can store 112 GB, but it can actually store 120 GB.

So I can't understand why this happens and should I worry about.

The Size column shows as 112 GB.

  • I edited my question because I have a feeling that how can my disk space turn from 116gb to 112gb .PS.I don't know if my disk space was 116GB before but today it shows 112GB disk space. – user244378 Sep 26 '17 at 10:39
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    112 Gi(B) = 120 GB! GiB to GB Conversion – klanomath Sep 26 '17 at 10:41

Apple measures gigabytes as 1,000,000,000 bytes (in the decimal system) for advertising purposes whereas dh properly uses binary, converted to decimal, which means it's actually 1,073,741,824 bytes.

If you take 120,000,000,000 (Apple's advertised capacity) and divide it by 1,073,741,824 you get 111.75 GB when properly measured in binary.

If you visit:


and scroll ALL the way to the bottom of the page, you can see footnote #1:

1. 1GB = 1 billion bytes and 1TB = 1 trillion bytes; actual formatted capacity less.

There's no need to worry.

The actual available space on the drive after formatting is always less than the advertised space of the drive itself. This is the case across file systems and operating systems, no matter if you're using macOS, Windows or Linux.

The fact that you're seeing different numbers at different times indicate that you're looking at the Avail column, which tells you how much free space you have. This number will change over time as you add and remove files and data from the drive. The Mac will do this without you knowingly saving/deleting files - for example due to swap space. Therefore no reason for alarm.

  • Yeah but the size column is 112GI not the avail column – user244378 Sep 26 '17 at 0:34
  • Super, this is to be expected if you have a 120 GB drive. – jksoegaard Sep 26 '17 at 9:10

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