All creatures that have less than one HD are considered to have one.

Normally the *Monster Manual* (or *Dungeon Master's Guide*) provides such information, but I am not sure which one... Creatures get good or bad scores according to their types...

[This document][1] provides what you need, also it states HD categories as 1 *or less*, 2, 3 etc...  


  [1]: http://www.d20resources.com/modern.d20.srd/creature.types/