Every number on this page is arithmetic you can check: Torchline budgets 6,400 XP per character at level 20 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
10,560
14,080
17,600
21,120
Standard — a real fight, rarely lethal
19,200
25,600
32,000
38,400
Hard — someone will probably go down
30,720
40,960
51,200
61,440
Brutal — a character can die here
46,080
61,440
76,800
92,160
These are effective-XP budgets: a group of monsters is multiplied up before it is compared against them, so a budget of 25,600 does not mean 25,600 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 14,080
A lone threat — about 14,080 XP each (×1 crowd multiplier)
Creature
Type
Size
CR
AC
HP
XP
Adult Blue Dragon
Dragon
Huge
16
19
225
15,000
Adult Silver Dragon
Dragon
Huge
16
19
243
15,000
Iron Golem
Construct
Large
16
20
210
15,000
Marilith
Fiend
Large
16
18
189
15,000
Planetar
Celestial
Large
16
19
200
15,000
A pair — about 4,693 XP each (×1.5 crowd multiplier)
Creature
Type
Size
CR
AC
HP
XP
Bone Devil
Fiend
Large
9
19
142
5,000
Clay Golem
Construct
Large
9
14
133
5,000
Cloud Giant
Giant
Huge
9
14
200
5,000
Fire Giant
Giant
Huge
9
18
162
5,000
Glabrezu
Fiend
Large
9
17
157
5,000
A group of four — about 1,760 XP each (×2 crowd multiplier)
Creature
Type
Size
CR
AC
HP
XP
Air Elemental
Elemental
Large
5
15
90
1,800
Barbed Devil
Fiend
Medium
5
15
110
1,800
Bulette
Monstrosity
Large
5
17
94
1,800
Earth Elemental
Elemental
Large
5
17
126
1,800
Fire Elemental
Elemental
Large
5
13
102
1,800
A swarm of eight — about 704 XP each (×2.5 crowd multiplier)