Deity Levels were first introduced in Season 3: Episode 7 of Epic Universe: Next Generations by Omniscience. They are practically a multiplier of Zeno's and Xamo's base power which makes both of their deity level equal to 1. For example, in the beginning of season 3 of Epic Universe: Next Generations, Weegee II's power in his Giga Form was about 45% of Zeno's base power. Therefore, his deity level would be 0.45.
The way to calculate characters' deity level is by using this formula:
137,150,000,000,000,000 / Power Level = Deity Level
The way to calculate characters' power level through their deity level is by using this formula:
Deity Level / 137,150,000,000,000,000 = Power Level