The Superhero Database Classification number, or SHDB Class, is a number that represents the overall 'power' of a character. All traits of a character are used for calculating the Classification.
What it DOESN'T mean
This doesn't mean that a higher class would always beat a lower class character. But the bigger the difference in Class is, the more obvious it is who'll win in a fight.
How is this calculated
( INT^1.3 + (STR*0.5 )^2 + (SPE*0.5)^2 + DUR^1.6 + (POW + (SPS*SPL))^2 + COM^1.8 ) ^ TIER
Super Power Score and Level
Every Super Power has a score (SPS) that is used to calculate the Class. Each Super Power also has 3 levels (SPL). The level is set when connecting that Super Power to a character. The level determines the final score, of the Super Power, being used in the calculation.
^ He states that in his third fusion he "transcends both hollow and shinigami"
^ Aizen has knowledge on yamamotos power and with prep was able to negate his shikai by creating wonderweiss to absorb his flames, so if you think "I transcend hollow and shinigami" doesn't include yamamoto in bankai that would be surprising considering you'd have to severely downplay aizens intelligence in order to say he can't put a simple 10x multiplier on top of yamamotos shikai, aizen is literally the second smartest character in the soul society behind kisuke urahara
^ Monster Aizen is a huge power jump from 3rd fusion aizen considering 3rd fusion aizen was getting the beat down by post dangai ichigo whereas monster aizen could hurt him in 1 attack, pretty sure that aizen wins this fight