# what is 1K-blocks in df, and how to calculate Use percentage?

I have search many and not found `1K-blocks` meaning in df command(gnu), but I have calculated and think it equals to `1K Byte`? Is there a offical explanation?

Then how to calculate the `Used Percentage`?

For example:

``````tankywoo@gentoo-jl::~/ » df -h
Filesystem                   Size  Used Avail Use% Mounted on
/dev/sda3                     15G  5.9G  8.2G  42% /

tankywoo@gentoo-jl::~/ » df
Filesystem                  1K-blocks    Used Available Use% Mounted on
/dev/sda3                    15481840 6163320   8532088  42% /
``````

In my local machine, I know there is `reserved space`.

Used is 6163320, Avail is 8532088, so:

I think `Used%` should be (15481840-8532088)/15481740 = 44.88%, not 42%.

So how to get the result `42%`?

The 1K block in GNU coreutils df(1) means 1024 bytes. Confirmed by taking a quick look at GNU coreutils, version 8.13, source code:

``````964   if (human_output_opts == -1)
965     {
966       if (posix_format)
967         {
968           human_output_opts = 0;
969           output_block_size = (getenv ("POSIXLY_CORRECT") ? 512 : 1024);
970         }
971       else
972         human_options (getenv ("DF_BLOCK_SIZE"),
973                        &human_output_opts, &output_block_size);
974     }
``````

As you can see, default output block size is 1024, unless environment variable `POSIXLY_CORRECT` is set.

When calculating used percentage, df(1) subtracts reserved space/blocks for root user from the available space, when underlying filesystem supports reserved space/blocks (most do):

``````529   if (known_value (total) && known_value (available_to_root))
530     {
531       used = total - available_to_root;
532       negate_used = (total < available_to_root);
533     }
``````

To sum this up, the official authority in this and every case is the source code.

• OK, thank you very much, I have read the source code and find the calculation: `pct = u100 / nonroot_total + (u100 % nonroot_total != 0);` Jan 27, 2014 at 16:07