There are two types of power scalings within the novel. One for the monsters and one for the humans.
Humans : F Class to S++ Class
F Class: 1st circle to 2rd circle magic or battle aura
E Class: 3th circle to 4th circle magic or battle aura
D Class: 5th to 6th circle magic or battle aura
C Class: 7th circle magic or battle aura
B Class: 8th circle magic or battle aura
A Class: 9th circle magic or battle aura
S Class: 10th circle magic or battle aura
S+ Class: 11th circle magic or battle aura
S++ Class: 12 circle magic or battle aura
S+ and S++ classes are extremely hard to reach and can only be done by a handful of powerhouses within each kingdom in the vast continents
Monters:
Power system is the same except the weakest monsters are equivalent to E Class magicians because they can absorb more mana from the surroundings and cultivate more effectively
Also, for the monsters,
S+ Class : Millenial Beasts
S++ Class: Myriad Beasts
For all races:
Demigod Class: One of the strongest existences on the planet