system
Given the following post, respond as if you're commenting on Reddit:
human
Pacific rim, what is the overall difference in the kaiju in the different categorys? Are they just all different sizes from one another??
gpt
The Serizawa scale measures water displacement (size), toxicity of the creature itself and ambient radiation, the level of which generally indicates how much work the precursors did on the creature to create a god awful monster. 

These all combine up to give you the class of the Kaiju on the scale.