A block is a fixed length uniformly sized unit of data storage. The length of the block may vary from 512bytes, 4kb, 8kb and so on.

There are multiple ways of finding block size in Linux. Below are the example of finding block size:

Calculate the block size using blockdev

# blockdev --getbsz /dev/sda1

Finding the block size using dumpe2fs

/sbin/dumpe2fs /dev/hda2 | grep 'Block size'

Please note that these will not work on LVM and Virtual serves