Class levels and Challenge rating

[Pesimismrocks]

I will soon be running my first oneshot. It was probably explained in the DM's Guide but Ive re-read the section on class levels but I don't really understand how they interact with challenge rating. I am building two characters a dwarven wizard and an awakened bear monk, but I dont understand how many class levels I shold give each, I want the wizard and bear to win but not to wipe the party out instantly. Any ideas on how many levels I should give them and what builds. The party will be 4-5 level 8s. They will be quite new to 3.5, but have played 4e and AD&D before. Any help is aprreciated.

[Sylthia]

Is there a plot reason you want the PCs to lose? As a DM I will often try to make a battle challenging, but not outright try to beat the PCs unless there is a plot reason or the party is being foolish. To answer your question, a well equipped level 11 party of 2 should be able to just barely beat that party by the book, but it will depend on how the rolls go.

[Urpriest]

First of all, you should read my Monster Handbook, which discusses this in detail. If you don't know how to give a monster with class levels a challenge rating then probably there are other things you need to learn as well.

To summarize the part you want to know, it depends whether the monster race you're using has racial hit dice or not. Dwarves have no racial hit dice and no special bonuses to CR, so their CR is equal to their character level (if they're using PC classes) or character level -1 (if they're using NPC classes like Adept). If the monster has racial hit dice, you need to think about whether the class they're taking is associated or nonassociated, basically, whether it is supported by the monster's stats or not. Monk doesn't tend to be an associated class for anybody, so Monk levels only add 1/2 to CR until you have as many Monk levels as Racial Hit Dice, then they add 1 to CR per level after that.

[Pesimismrocks]

Is there a plot reason you want the PCs to lose? As a DM I will often try to make a battle challenging, but not outright try to beat the PCs unless there is a plot reason or the party is being foolish. To answer your question, a well equipped level 11 party of 2 should be able to just barely beat that party by the book, but it will depend on how the rolls go.

They're bith good parties and there is an intentional misunderstanding which is why I want the wizard and bear to subdue the party. Thanks for the advice on level too..

Also thanks Ur-Priest for the guide, particularly as this is my first time DMing, very useful for my other encounters. The bear does have 6 racial hit dice, they're quite powerful too for animal hit die