Every number on this page is arithmetic you can check: Torchline budgets 180 XP per character at level 3 for a standard fight, scales it by party size, then by the difficulty band. Below each table are the SRD 5.1 creatures that actually land in that budget.
Budgets by party size and difficulty
Difficulty
Party of 3
Party of 4
Party of 5
Party of 6
Skirmish — resources barely dented
297
396
495
594
Standard — a real fight, rarely lethal
540
720
900
1,080
Hard — someone will probably go down
864
1,152
1,440
1,728
Brutal — a character can die here
1,296
1,728
2,160
2,592
These are effective-XP budgets: a group of monsters is multiplied up before it is compared against them, so a budget of 720 does not mean 720 XP of monsters.
What actually fits, for a party of four
The crowd multiplier is the part that catches people out. Two creatures count for 1.5× their XP, three to six count double, seven to ten count 2.5×, eleven or more count triple. So the XP you can spend per creature falls fast as the group grows.
Skirmish — budget 396
A lone threat — about 396 XP each (×1 crowd multiplier)
Creature
Type
Size
CR
AC
HP
XP
Ankheg
Monstrosity
Large
2
14
39
450
Awakened Tree
Plant
Huge
2
13
59
450
Azer
Elemental
Medium
2
17
39
450
Bandit Captain
Humanoid
Medium
2
15
65
450
Berserker
Humanoid
Medium
2
13
67
450
A pair — about 132 XP each (×1.5 crowd multiplier)
Creature
Type
Size
CR
AC
HP
XP
Ape
Beast
Medium
1/2
12
19
100
Black Bear
Beast
Medium
1/2
11
19
100
Cockatrice
Monstrosity
Small
1/2
11
27
100
Crocodile
Beast
Large
1/2
12
19
100
Darkmantle
Monstrosity
Small
1/2
11
22
100
A group of four — about 50 XP each (×2 crowd multiplier)
Creature
Type
Size
CR
AC
HP
XP
Acolyte
Humanoid
Medium
1/4
10
9
50
Axe Beak
Beast
Large
1/4
11
19
50
Blink Dog
Fey
Medium
1/4
13
22
50
Boar
Beast
Medium
1/4
11
11
50
Constrictor Snake
Beast
Large
1/4
12
13
50
A swarm of eight — about 20 XP each (×2.5 crowd multiplier)