What is a link between bad-blocks % and bad-blocks count?

This url is about count.
http://wiki.mikrotik.com/wiki/Manual:Ro ... bad_blocks
But latest routeros shows %

uptime: 2w2d2h21m59s
version: 5.4
free-memory: 234852KiB
total-memory: 256552KiB
cpu: e500v2
cpu-count: 1
cpu-frequency: 799MHz
cpu-load: 8%
free-hdd-space: 471748KiB
total-hdd-space: 520192KiB
write-sect-since-reboot: 530863
write-sect-total: 605591
bad-blocks: 0.3%
architecture-name: powerpc
board-name: RB800
platform: MikroTik

Is it a normal state 0.3% bad-blocks?

Yes, it is normal. NAND memory manufacturers already ship these memories with some bad blocks (that is indicated by some letter/digit in serial number),
As long as that number is stable and below few percents - you are fine.

thanks