Fraction Challenge Ratings

Rules Questions

How exactly do you calculate fraction challenge ratings like CR 1/3 Drow?

For example I want to have players early in my campaign fight 3 Drow and I am wondering would the total CR for this brawl be 3 and a third or 1?

Check the experience amount given per creature, multiply by the number of creatures, and compare back to the experience per CR chart. In this case it's 135 XP per CR 1/3 Drow. Three of them combined is just a little more than 400 XP (it's 405 XP, which is probably due to them not wanting to use 133 XP each), so it's a CR 1 fight.

It would be approximately a CR 1. Look at the XP totals. 3 CR 1/3 creatures is 405 xp. A CR 1 encounter is 400 xp. If you want to throw a CR 3 encounter at the party, it should add up to 800 xp worth of monsters. a CR 1/3 is 135 xp, so you would need about 6 of them (its technically 810 xp, but that is close enough).

That is the best way to look at it. The table for multiple monsters = CR + # gets screwy when dealing with CR < 1 in my experience.