If you have no other ways of finding out what is the size in bytes of the blocks of a filesystem (don't have any other utilities giving you this information), it is very easy to find this out on your own. This solution was provided by OSOR on LinuxQuestions.org - thanks a lot!
Write a file called blocks.c with the following C-source text in it:
Compile the whole thing with make blocks and run the program - e.g. "./blocks /dev/hda1".
fsutil fsinfo ntfsinfo
Have a look at the value of "Bytes Per Cluster".