The operating system allocated 4096 bytes for the folder "file", and that is the size displayed by Thunar.
As described in #61 (closed), the amount of items inside the folder could be shown instead.
There is as well an issue for showing the recursive size instead: #94 Though on ext3/ext4 that can be expensive in terms of performance / might take a while if you open up root (No idea how it works for other file systems).
Feel free to port the attached patches to master, if you can, and fix the remaining issues, so they can be merged one day !
Closing this issue as a duplicate.
closed
mentioned in issue #94