Spell vamp

Spell vamp is a magic stat that works as a counterpart of life steal. However, instead of regenerating health based on basic attacks, the regeneration of health 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. See also: list of effects that apply or don't apply spell vamp.

Champion abilities
Note: ''Only the effect regarding the spell vamp of this abilities is shown. For full description and detail visit each champion page''
 * grants 35% spell vamp for the next spell upon reaching 9 charges of Essence Theft.
 * grants 6% spell vamp, increasing by an additional 1% for every 6 bonus attack damage gained thereafter.
 * grants spell vamp.
 * grants spell vamp.
 * grants him spell vamp for 6 seconds.
 * grants spell vamp.

Masteries

 * grants spell vamp and life steal.

Runes

 * Quintessences of grant  spell vamp.

Ability Drain
Note: ''These abilities will heal the champion by a percentage of the damage dealt from their ability. These act similar to how spell vamp works.''
 * heals for of the damage dealt.
 * heals for 20% of all damage dealt to enemies, from any source, within the ability's radius.
 * heals for 10% (25% against champions) of the damage dealt.
 * heals for 100% of the damage dealt.
 * heals for 5% of the damage dealt. The heal from this ability is capped at . The healing is doubled and the cap is tripled if he has more than 50 fury.
 * heals for 25% (75% against champions) of the damage dealt.
 * heals for 100% of the damage dealt.
 * heals for 80% of the damage dealt.
 * heals for 12% of the damage dealt.
 * heals for 40% of the damage dealt.

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 (armor for physical damage or magic resistance for magic damage):
 * 25% spell vamp on a single-target spell that does 100 damage will return 1000.25125 health.
 * 25% spell vamp on an AoE spell that does 100 AoE damage to each of 4 targets will return 41000.25(13)33.3 health.

Trivia
The currently optimum spell vamp is  attainable on Akali using her. This requires:
 * Attack Damage sources
 * 200 AD - 2 x (fully stacked)
 * 110 AD - (fully stacked)
 * 40 AD -
 * 40 AD -
 * 10 AD -
 * 8 AD - nearby (aura)
 * 23 AD -
 * 50 AD -
 * 20 AD -
 * 35 AD -
 * 5 AD - with
 * 39.25 AD - Marks of, Seals of Might and Glyphs of Might
 * 3 AD -
 * 9 AD -
 * Total AD: 592 AD (note that the first 10AD equates to 8%)
 * Conversion: (592 - 10) / 6 = 97.04%
 * Total: 105.04%


 * Spell Vamp sources
 * 20% -
 * 20% -
 * 20% - nearby allied (aura)
 * 6% - Quintessences of
 * 3% -
 * Total: 69%


 * doesn't increased the given spell vamp, but improves the healing to an effective subtotal of 174.04% to 209%.