There are many ways to achieve this.

1.Via smitty:

Add / Change / Show / Delete File Systems
=> Journaled File Systems
=> Change / Show Characteristics of a Journaled File System
=> Select the file system you want to see

2. With lsfs -q, one block size is 512 bytes so in our example, the filesystem block size is 2kb:

gzaix@root:/ # lsfs -q .
Name            Nodename   Mount Pt               VFS   Size    Options    Auto Accounting
/dev/lv_BLAH   --         /oracle/BLAH          jfs2  524288  rw         yes  no 
  (lv size: 524288, fs size: 524288, [color=green]block size: 4096[/color], sparse files: yes, inline log: no, inline log size: 0, EAformat: v1, Quota: no, DMAPI: no, VIX: yes, EFS: no, ISNAPSHOT: no, MAXEXT: 0, MountGuard: no)

3. With echo and ls, again the value is 2kb:

Add one character into a file and the file's will occupy exactly one block. Simple, no? :)

gzaix@root:/ # echo b >tmp.tmp
gzaix@root:/ # ls -l -s tmp.tmp
   4 -rw-r--r--    1 root     system            [color=green]2[/color] Feb 25 13:14 tmp.tmp