The rules for encounter building and XP rewards in PF2E are great. If your party is all about the same level and you know how difficult of an encounter you want to throw at them it’s really easy to build that encounter. As in so many things, the core Pathfinder math Just Works.
But what is hidden behind it? What if, due to player shenanigans, the encounter ends up being very different than you planned or there is a completely unplanned combat? Or you’re just curious about how the encounter math works behind the scenes?
Well, here’s how it works: Creatures of level 1 and above are worth 160 XP/level. So, a level 2 creature is worth 320 XP and a level 10 is worth 1600 XP. Creatures of level -2, -1 and 0 are worth 40, 80 and 120XP respectively.
To get the per character XP reward for defeating the encounter, total the XP for the creatures in the encounter and divide by the total PC levels at the table.
For example: an encounter of one level 2 and two level 1s is worth 640XP. If faced by a four person party each of level two, thats 640/(4 * 2) = 80XP per character. Or that same 640XP encounter by a party of two level 2 and one level 1? 640/(2+2+1) = 128XP per character.
Granted, this can get silly if the creature levels are way out of whack, which is why in the encounter building rules they don’t have table for creatures more than ±3 levels away from the PCs. But just in case you have an odd party or an odd encounter, the math is pretty easy.
Hmm. Something seems a little out of wack, as XP doubles every 2 levels, but you’re scaling things linearly here. One Level 1 creature is worth 40 XP to a combat vs a group of 4 Level 1 PCs, so things work out here. But a Level 2 creature is worth 60 XP, not 80, and 60 * 4 = 240, not 320.
If you’re indexing the creature XP to Level 1, the XP curve looks like this (where Approx XP uses a 240 baseline for Level 2 as they do in the books, and XP is using exact scaling):
Level XP Approx XP Linear Scaling 1 160.0 160 160 2 226.3 240 320 3 320.0 320 480 4 452.5 480 640 5 640.0 640 800 6 905.1 960 960 7 1280.0 1280 1120 8 1810.2 1920 1280 9 2560.0 2560 1440 10 3620.4 3840 1600 11 5120.0 5120 1760 12 7240.8 7680 1920 13 10240.0 10240 2080 14 14481.5 15360 2240 15 20480.0 20480 2400 16 28963.1 30720 2560 17 40960.0 40960 2720 18 57926.2 61440 2880 19 81920.0 81920 3040 20 115852.4 122880 3200 21 163840.0 163840 3360 22 231704.8 245760 3520 23 327680.0 327680 3680 24 463409.5 491520 3840 25 655360.0 655360 4000 26 926819.0 983040 4160 27 1310720.0 1310720 4320 28 1853638.0 1966080 4480 29 2621440.0 2621440 4640 30 3707276.0 3932160 4800 Using Level 1 indexed XP (let’s call it XP_1, for the sake of brevity), your example above becomes 560 XP shared between either 4 equally levelled characters (140 XP) or 3 unequally levelled ones, with it being unclear how exactly to divvy up the reward.
I’m not convinced your use of level as weight works, due to the fact that level power does not scale linearly. Instead, I would look to the players’ contribution to the party’s XP pool. PCs have an encounter XP budget that’s the same as monsters’, by level, which means the mixed party has 160+240+240 = 640 XP between them. The Level 1 character contributes 160/640 = 0.25, or 1/4 of the party’s XP, so they should probably receive 1/4 of the XP reward.
560 * 0.25 = 140 XP, which is what they would get if it was a party of 4 Level 1 PCs.
The other two characters each contribute 37.5% of the party’s XP, so they would each receive 560 * 0.375 = 210 XP, which would scale to 150 XP in the standard rolling XP window.
I’ve been kicking this math around for a while now on scrap paper. There’s been a small spike in questions around XP and balance over on r/Pathfinder2e, though, so maybe I’ll work through his a little and make it a little more accessible/searchable.
