How do I calculate the Challenge Rating of a PC?

Challenge rating has always confused me, considering CR of a monster assumes a party of 4. However, when i'm not doing organised play I most often end up playing with 2-3 people, a very small group to DM. I'm curious as to how one level of monster CR compares to one class level. If I have a level 1 character, what would his CR be if he were a monster? How do I calculate it? Also, how much would a creature's CR be effected if it became a vampire or lycanthrope?

The guidelines for calculating a challenge rating begin on page 274 of the Dungeon Master's Guide. If a creature becomes a lycanthrope or vampire, apply any modifiers from the monster description, then calculate the challenge rating as usual using the methods outlined in the DMG.

If you are coming from an earlier edition of D&D that used challenge ratings, please note that while the terminology has remained, its meaning is very different than it was before.

For a description of what the term "challenge rating" means in 5th Edition, see page 9 of the Monster Manual.

You don't really need to look at the CR of an individual character to ehlp you out, but if you want to, you can run the PC through the DMG's CR calculator.

If you're not trying to over optimize, I've found the fighter to be like CR 1/2 at 1st level. That's a fair assessment, since 4 CR 1/2s vs. 4 level 1 PCs would be a ridiculous fight at first level.

If you're trying to figure out how to deal with a smaller party without powering people up, the DMG has the rules for it. You modify the "xp multiplier" for the number of foes. For a 3 person party, you drop all of the levels down, so 1 monster is x1.5 xp.

I have done this for some classes and levels; here are my results, and an example of my process.

[sblock="Wizards"]Wiz 1 - CR 1/2: DCR 1/4, OCR 1
Wiz 2 - CR 1: DCR 1/4, OCR 2
Wiz 3 - CR 1: DCR 1/4, OCR 3
Wiz 4 - CR 2: DCR 1/4, OCR 4
Wiz 5 - CR 5: DCR 1/4, OCR 11

Note that the character is still Defensive CR 1/4 at 5th level. I was using the spell list from the MM "mage," which includes mage armor, but not shield, and no relevant 2nd-level spells. Fireball is fireball, but this dude won't last one round in a straight fight. The Eternal Flame Priest from Princes of the Apocalypse is a good firebally guy (though it has the same AC and twice as many HP as my wizard stat block, and is listed as CR 3. Hmm....)[/sblock]

[sblock="Fighters"]Ftr 1 - CR 1/2: DCR 1, OCR 1/2
Ftr 2 - CR 1: DCR 1, OCR 1/2
Ftr 3 - CR 1: DCR 1; OCR 1
Ftr 4 - CR 2; DCR 2, OCR 2
Ftr 5 - CR 3; DCR 4, OCR 3
Ftr 6 - CR 4: DCR 4, OCR 4
Ftr 7 - CR 4: DCR 4, OCR 4
Ftr 8 - CR 5: DCR 5, OCR 5
Ftr 9 - CR 6: DCR 6, OCR 5

This is for a sword-and-shield Fighter with all the simplest options. Stats are the standard array with no racial modification. Armor is upgraded at higher levels, but no magical items. Any of these factors can potentially change the CR.[/sblock]

[sblock="Two Examples"]
Note: These examples use a homebrewed race and futuristic weapons, so these results are not correct for PHB characters. Maybe I'll post the stat blocks in the homebrew forum, but this is just for an example of the process of applying the monster math to characters.

The Maverick is an 11th-level Fighter with the following options:
Stats before racial adjustment: Str 15, Dex 15, Con 15, Int 8, Wis 8, Cha 8
Level 1: Great weapon fighting
Level 3: Champion
Level 4: Great weapon mastery
Level 6: +1 Str, +1 Con
Level 8: +2 Str
Level 10: Defense

Before calculating CR, I have to do some math regarding the Great Weapon Master feat.

First of all, should the Maverick use regular attacks or power attacks? Assuming 3 attacks, regular attacks give you 90 DPR at +9. That's OCR 14. Power attacks give you 120 DPR at +4. That's CR 19 damage, modified down for the low attack bonus, yielding OCR 16. Is a power attack really 2 levels better than a regular attack? I'm not sure, but the versatility seems worth it. I'll calculate as if the Maverick is always using power attacks.

Second, how often will this fighter get to cleave? Assuming one use of Action Surge, the Maverick will attack 12 times. Based on a formula that I found on some forum [(18/20)^12], the Maverick has about 71.6% to get a critical hit. Add the possibility of knocking down one of the PCs or their allies, and it seems safe to assume one cleave attack during the first 3 rounds.

So, 13 attacks, for an average of 173.3 DPR at +4. That translates to OCR 19. Damn.

Of course, that's assuming the Maverick is attacking with its sword every turn. If we restrict it to the antimatter rifle, it's 12 attacks, for an average of 64 DPR at +7. That's OCR 10.

As for defenses: AC 19, 155 hp. DCR 8.

Total CR 13 in melee, 9 at range.

***

The Hunter is an 11th-level Fighter with the following options:
Stats before racial adjustment: Str 15, Dex 15, Con 15, Int 8, Wis 8, Cha 8
Level 1: Archery
Level 3: Champion
Level 4: Sharpshooter
Level 6: +1 Dex, +1 Con
Level 8: +2 Dex
Level 10: Defense

Assuming one use of Action Surge, that's 12 attacks in the first three rounds. Power attacks are better than regular attacks, so I use those; 112 average DPR at +6 gives me OCR 16.

Of course, that's assuming it's using the laser rifle. If we're talking melee with beam shortswords, we're talking 14 attacks, for an average of 66.6 DPR at +9. The DMG gives me OCR 11.

Assuming Second Wind and full regeneration, the Hunter has 155 hp and AC 19. DCR 8.

So, all together, that's CR 12 at range, and 9.5 in melee.[/sblock]

The easiest way is to take the XP reward of a creature equal to the players level, divide by four, then reference the CR for that new amount of XP. For example, a level 5 player, take XP for a CR 5 creature (1800), divide by 4 (450), and that's CR 2. Example 2: player level 10, CR 10 XP (5900), divide by 4 (1425) = ~ CR 4.5. This is based on reversing formula that a party of four finds CR to be a fair challenge.

It's easy, but it's not necessarily the most accurate. Because many PCs can go nova in ways monsters often can't. To be the most accurate, use the DMG method and calculate damage based on the PC going nova.

Cr equals lvl

CR does not equal level in 5E.

CR has nothing to do with 4 PCs (or any other number of PCs) in 5E.

CR is based on set ranges of numbers: average damage, proficiency bonus, AC, hit points, save DC. You determine the CR of a PC the same way you would determine the CR of a custom monster--by determining those numbers, and seeing where they fall on the custom monster chart, adjusting accordingly.

And yes, that means two characters of the same level might have wildly different CRs, based on armor, damage dealt, spells known, etc.

Interesting topic. For encounters, i often roll up monsters as PCs. Like 5th level kobold barbarians against the 5th level party... it really depends on what the intent of the encounter is. But one thing for sure, my players never assume something is going to be a cakewalk to fight and it a possible threat upon their life (they play and fight smarter too). Anyway, I never thought to put a CR on them. I think i'll check that it out, out of curiosity.