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
The most important feature for the SHDB Class is Intelligence. Second is Power. Speed, strength and durability are about equal important. Every Superpower also has different influence on the characters 'power' trait. For example: a character gets more points for being Immortal than having the ability of Flight.