Spell Power

Spell power rating determines how much damage you deal with spells. In most cases, each point of spell power increase increases the base damage of your spell by 1 %. Various effects can contribute to your spell power, all effects are added together.

Spell power was introduced in Update 14 and replaced previous spell damage amplification that involved addition and multiplication.

This concept applies only to spells that cause hit point damage and spells that heal hit points.

Sources of spell power
Class Enhancements, such as Cleric Life Magic or Sorcerer Fire Manipulation.
 * Spell power increases from different enhancement lines stack. E.g.: Druid Eminence of the Sun I + Artificer/Sorcerer/Wizard Flame Manipulation I = 60 Fire/20 Light spell power)

Metamagic feats (spell power increases from metamagic feats stack)
 * Empower Healing Spell +75
 * Empower Spell +75
 * Maximize Spell +150

Magic items
 * Equipment bonus from items with enchantments like Potency or Combustion. The item enchantment name corresponds to the type of spells the spell power applies to. The equipment bonus on randomly generated loot increases on higher level equipment. (See Thaumaturgy for an overview table.)
 * Combustion = Fire
 * Corrosion = Acid
 * Devotion = Positive (Healing)
 * Glaciation = Cold
 * Impulse = Force, Untyped, Slashing, Piercing, Bludgeoning, (Bane?)
 * Magnetism = Electricity
 * Nullification = Negative
 * Potency = Universal
 * Radiance = Light, Alignment
 * Reconstruction = Repair, Rust
 * Resonance = Sonic
 * Implement bonus from caster weapons (equal to 3 * enhancement bonus of the weapon)
 * Effects that increase the enhancement bonus also increase the implement bonus, e.g. Artificer Enchant Weapons or Druid Magic Fang.
 * Alchemical bonus from clickies, e.g. Inferno. The item enchantment name corresponds to the type of spells the spell power applies to:
 * Ardor = Positive (Healing)
 * Brilliance = Light, Aligned
 * Cacophony = Sonic
 * Efficacy = Universal
 * Erosion = Acid
 * Freeze = Cold
 * Impact = Force, Untyped, Slashing, Piercing, Bludgeoning
 * Inferno = Fire
 * Mending = Repair, Rust
 * Nihil = Negative
 * Spark = Electricity
 * Psionic bonus from e.g. Xachosian Eardweller

Epic Destiny bonuses (e.g. Dragon Heritage), usually stacking with everything else

Exceptions
Some spells receive limited (usually half) benefit from spell power:
 * Heal: 50%
 * Mass Heal: 50%
 * Necrotic Touch (Pale Master): 50%
 * Necrotic Bolt (Pale Master): 50%
 * Necrotic Blast (Pale Master): 50%
 * Arcane Bolt (Archmage): 50%
 * Arcane Blast (Archmage): 50%
 * Summon Archon (Favored Soul): 50%
 * All Runearm Shots: Between 50% and 80%
 * Reconstruct will be added to this list with Update 15

Heal and Mass Heal spells still receive full benefit from the Empower Healing Spell feat.