Each spell level utilizes a different die when calculating damage. The table per spell level is as follows:

The dice below are multiplied by caster level (plus miscellaneous bonuses) to determine spell damage.

Note: Some spells do not strictly adhere to this table, but typically will note their altered effects

Note: Spells with 'fixed' spell levels will use damage dice based on the fixed level instead (typically for healing).

All classes:

Splash Spell: -1 level
Burst Spell: -2 levels

Various feats and conditions may shift the damage table further.

Area of effect: rolls : 1 + clevel / 2 dice (spell level sized dice) (always d6 for warlock/monk)

Monks:
1d11 for all spells

Warlocks:
1d11 for all spells, 1d12 for utterdark spells