The initial critical blow strength is 220% of the basic (white) damage.
So, if your basic attack inflicts 100 damage, then your critical blow will inflict 220 damage
For example:
If you’ve received an effect that will increase your critical blow strength by 50%, then the total amount of critical damage will be 270% of your basic (white) damage.
Then, if your basic attack inflicts 100 damage, your critical blow will inflict 270 damage