CR of NPC Classes

[EOL]

I'm sure this has been brought up and it's probably in the DMG somewhere (though not in the section about NPC classes), but what formula should be used to assign a Challenge Rating to someone with some levels in either adept, aristocrat, commoner, expert, or warrior. For a "normal" class it's relatively easy character level=CR, but what should it be for NPC classes. For some reason (maybe I read it somewhere) I'm inclined to go with 2/3 (NPC level)=CR.

Thoughts? Chapter and Verse?

 

[Dr. Zoom]

DMG, page 167.

CR is level -1. A first level NPC's CR is 1/2. Monsters with NPC levels add NPC level -1 to the CR of the monster, with a minimum of +1.

 

[EOL]

Thanks I knew it had to be in there somewhere this is just the first time I've had my party fight a commoner...

 

[rankarrog]

Although the official formuala for NPC-Class-CR is Classlevel-1, I'd go with Classlevel/2 for the Commoner at least (A Commoner is a worse fighter than a wizard of the same Level(can only use one weapon, can only spend money to buy a half...))