If you want to know the blocksize of your file system you can check this in multiple ways. One of the most commonly used ways is to execute the below command:
dumpe2fs /dev/sda1 | grep -i 'Block size'
this calls dumpe2fs, prints the super block and blocks group information for the filesystem present on device. in the above example we gather the information of /dev/sda1
As you can see we do a grep on 'Block size'. If you do not grep this you will get a LOT of information. the most usable for most users is the first part. You can simply use a more to get this information in the most easy way:
dumpe2fs | more
as an example you can see the output of this below which is the information of one of my workstations:
dumpe2fs 1.42 (29-Nov-2011) Filesystem volume name:
Last mounted on: / Filesystem UUID: 584232d2-3bc8-41bb-9534-c3a4f4f6e64c Filesystem magic number: 0xEF53 Filesystem revision #: 1 (dynamic) Filesystem features: has_journal ext_attr resize_inode dir_index filetype needs_recovery extent flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize Filesystem flags: signed_directory_hash Default mount options: (none) Filesystem state: clean Errors behavior: Continue Filesystem OS type: Linux Inode count: 91054080 Block count: 364187648 Reserved block count: 18209382 Free blocks: 337917734 Free inodes: 90742705 First block: 0 Block size: 4096 Fragment size: 4096 Reserved GDT blocks: 937 Blocks per group: 32768 Fragments per group: 32768 Inodes per group: 8192 Inode blocks per group: 512 Flex block group size: 16 Filesystem created: Sat Dec 31 17:42:47 2011 Last mount time: Sun Sep 9 20:37:55 2012 Last write time: Wed Apr 11 17:52:11 2012 Mount count: 11 Maximum mount count: 21 Last checked: Wed Apr 11 17:52:11 2012 Check interval: 15552000 (6 months) Next check after: Mon Oct 8 17:52:11 2012 Lifetime writes: 225 GB Reserved blocks uid: 0 (user root) Reserved blocks gid: 0 (group root) First inode: 11 Inode size: 256 Required extra isize: 28 Desired extra isize: 28 Journal inode: 8 First orphan inode: 70780693 Default directory hash: half_md4 Directory Hash Seed: c55ef959-1938-4934-b178-eb9409c00d0b Journal backup: inode blocks Journal features: journal_incompat_revoke Journal size: 128M Journal length: 32768 Journal sequence: 0x00102c0c Journal start: 30520