File sizes are calculated in Kibibytes, but the UI says Kilobytes.

As stated on the International System of Units (the metric system),
1k = 1000, for any unit.
1kB = 1000B

Since in computing, 1024 is used a lot, Kibibytes and Mebibytes where created;
1KiB = 1024B
1MiB = 1024*1024B

Thunar uses the definition of Kibibytes for calculation, but the UI says
Kilobytes.  This results in the wrong data being presented to the user, with
about 2% error margin for kilobytes, slightly more for megabytes, and notably
more for gigabytes (~8%), and so on exponentially.
And so on.

Please see the following articles for more information:
http://en.wikipedia.org/wiki/International_System_of_Units
http://en.wikipedia.org/wiki/Kibibyte