Spell vamp

Spell vamp is a magic stat. The spell vamp works as a counterpart of life steal, but instead of regenerating health based on autoattacks, the regeneration is based on damage done by champion abilities. It works off of activated item effects, summoner spells, and abilities, regardless of the type of damage done. Spell vamp is calculated from the damage dealt to the enemy after reductions such as magic resistance, armor or effects like. It stacks additively, and has no cap.

Champion abilities

 * grants 35% spell vamp for the next spell upon reaching 9 charges of Soul Eater.
 * grants 8% spell vamp when she obtains 10 bonus attack damage, increasing by an additional 1% for every 6 bonus attack damage gained thereafter.
 * grants 5 / 10 / 15 / 20 / 25 % spell vamp.
 * grants 10 / 20 / 30 % spell vamp.
 * increases his damage based on his health and grants him 9 / 12 / 15 / 18 / 21 % life steal and spell vamp for 6 seconds.
 * grants 15 / 20 / 25 % spell vamp.

Calculations
The amount of health restored with Spell Vamp follows the following formula:
 * Health restoredtotal spell damagespell vampvamp coefficient

where
 * Total spell damage is the the mitigated spell damage done to every target affected, and
 * Vamp coefficient is 1 for single target spells and 1/3 for multi-target spells.

Examples
(Assuming targets with 0 pertinent resistance: Magic Resistance or Armor)
 * 25% spell vamp on a single-target spell that does 100 damage will return 1000.25125 health.
 * 30% spell vamp on an AoE spell that does 100 AoE damage to each of 4 targets will return 41000.30(13)40 health.

Trivia
The greatest spellvamp currently possible is with having 3 fully stacked, fully stacked , , , another  aura from a teammate,  aura,  aura and Marks, Seals and Glyphs of Might along with Quintessences of Transmutation. It amounts to (110 + 100*3 + 40 + 20 + 8 + 2.43 * 9 + 1.21 * 9 + 0.72 * 9 - 10) / 6 + 8 + 20 + 25 * 2 + 3 * 3 = 171.54% spell vamp.