Hit Points

Hit points, the number that keeps you from dying that are typically based on a combination of your Ability Scores and Class.

Hit points are an abstraction of how long someone can fight before falling unconscious or, possibly, dying.

Half charisma + half constitution to get your hit points at level 1.

Charisma should affect your hit points as your willpower keeps you fighting just as much as your ability to get hit would.

Size should also affect hit points?

The above chart shows the die that are used for each class to gain more hit points at higher levels. Certain subclasses may raise the die or lower it.