Every number on this page is arithmetic you can check: Torchline budgets 250 XP per character at level 4 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
413
550
688
825
Standard — a real fight, rarely lethal
750
1,000
1,250
1,500
Hard — someone will probably go down
1,200
1,600
2,000
2,400
Brutal — a character can die here
1,800
2,400
3,000
3,600
These are effective-XP budgets: a group of monsters is multiplied up before it is compared against them, so a budget of 1,000 does not mean 1,000 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 550
A lone threat — about 550 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 183 XP each (×1.5 crowd multiplier)
Creature
Type
Size
CR
AC
HP
XP
Animated Armor
Construct
Medium
1
18
33
200
Brass Dragon Wyrmling
Dragon
Medium
1
16
16
200
Brown Bear
Beast
Large
1
11
34
200
Bugbear
Humanoid
Medium
1
16
27
200
Copper Dragon Wyrmling
Dragon
Medium
1
16
22
200
A group of four — about 69 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 28 XP each (×2.5 crowd multiplier)