Class Levels and CR

[Bane-Wordsmith]

I've always written class levels to equal CR, but in some cases it just doesn't seem to add up. Would a single character, of the same level as a party of 4, really equal their challenge rating?
I understand that some classes are simply more powerful than others. But on average it just doesn't seem like they provide much of a threat.

How do you write the CR of encounters when it's human-like races with class levels their fighting?

[A_S]

Your previous thinking was correct: For PC-type opponents, CR = total class levels. For monstrous opponents, it can get more complicated (CR for added class levels depends on whether the levels improve what the base monster is already good at, or do a different thing; see Ur-Priest's handbook (http://www.giantitp.com/forums/showthread.php?207928-Urpriest-s-Monstrous-Monster-Handbook) for more details).

As for this seeming too easy: Remember that an opponent of equal CR to a party isn't supposed to provide a serious challenge to a party of 4. It's supposed to be an easy-to-moderate fight that consumes roughly 1/4 of the party's daily limited resources (spells, consumables, etc.). It's also supposed to be a challenge that a single PC of equal level has a roughly 50% chance of beating alone (this one is self-evidently true, since two PC-style characters of equal level are, other things being equal, obviously evenly matched).

This is because the game isn't designed around the idea that you have a substantial chance of losing every fight you get into. It's designed with the expectation that most of your fights are fairly easy, but challenging enough that you have to blow some consumables on them, and that you have about ~4 such encounters per day. Fights where you're actually supposed to have a decent chance of losing are assumed to be "boss fight" encounters, which generally have CR's a few levels above the party.

Not everybody plays the game this way, of course; some DM's and players prefer a grittier style of game where anybody could die at any moment. But it's not the base assumption of the designers.