Hit Points
Hit points measure how hard a character is to kill. Hit points mean two things in the game world: the ability to take physical punishment and keep going, and the ability to turn a serious blow into a less serious one.
Effects of Hit Point Damage
At 0 hit points, a character is disabled.
At from -1 to -9 hit points, a character is dying.
At -10 or lower, a character is dead.
Calculating Hit Points
A character gains additional Hit Points each time they purchase a level in a class. Hit points are calculated in the following way:
The Classes' listed Hit Dice + your Constitution modifier + your Fortitude saving throw bonus.