Spell power

Spell power is an attribute that increases the effect of spells. Spell power increases the damage amount of damaging spells and the healing amount of healing spells. Prior to Patch 3.0.2, the attribute known as spell damage would only increase the effects of damaging spells. Healing spells were only increased by the healing attribute. As of Patch 3.0.2, spell power now affects both types of spells. Nevertheless, there are items which can increase your bonus healing independently of damage spells. Similarly, there are items which grant bonuses only to certain magic schools such as fire or nature.

As of Patch 4.0.1 the ability to downrank has been removed. As well, spell power has been removed from Wrath of the Lich King gear (except weapons and trinkets) and gems, but casters now gain 1 spell power per point of intellect. Spell power on gems was changed to intellect; for example, +23 spell power became +20 intellect.

Information about spell power can be found on the Character tab of the Character info window under the Spell heading. The Bonus Damage attribute represents your spell power's contribution to general spell damage. Hovering your mouse over this attribute will show you the specific bonus damage for individual schools of damaging magic. These are typically equal to or greater than the base Bonus Damage attribute. The Bonus Healing attribute represents your spell power's contribution to healing spells. As with damage schools, this attribute is typically equal to or greater than your general Bonus Damage attribute.

Players often refer to this attribute as simply +damage, +dmg, or plus damage. For effects that target a specific school, it is similarly referred to by that school such as +fire. In particular, healers commonly refer to items with only a healing bonus as +healing.

Your bonus damage and bonus healing from spell power do not usually apply directly to a spell. Each spell (or each component of each spell) which causes damage or healing has a spell power coefficient which determines how much of your bonus damage or bonus healing will be applied to the spell. The coefficient may be more or less than 100%, depending on various spell factors. Rules for calculating the coefficient are discussed in the sections that follow.

Sources of spell power
Spell power is found primarily on equippable items, but can also be increased with potions, buffs and some class talents. Items with the following item suffixes will add spell damage or healing:

All spell damage and healing gains stack. The total bonus is determined by adding individual bonuses from all equipped items, all buffs, and any talents. The total amount of spell damage and healing can be tracked on the character sheet, under the Spell tab. Bonus Damage shows the total amount that applies to all schools. Mousing over Bonus Damage will break down the benefit by magical school, which includes items that only affect one school. Bonus Healing shows the amount that will be applied to healing spells.

Spell coefficients
How much that spell power contributes to the effect of a spell varies from spell to spell. It is generally related to the cast time and/or the duration of the spell, and different categories of spells have different formulas for calculating their spell power. The portion of your spell power which is contributed to a particular spell is referred to as the spell power coefficient. It typically does not vary within the same spell, but the lowest and highest ranks of some spells have different casting times or durations, which can cause the coefficient to be different for those ranks.

The spell power typically varies with either the spell's casting time, duration, or both. In general, spells with short casting times or short durations are less powerful and consume less mana than those with longer casting times and durations. The intention is for the coefficient to scale with the overall power of the spell being cast. That is, a spell which heals for 100 should receive less benefit than a spell which heals for 1000. If they received the same benefit, it would be far more efficient to "spam" small spells to get the same amount of free bonus damage/healing as you would get for casting the larger spell. Scaling the spell power coefficient helps preserve the base mana efficiency of spells.

That said, the correlation between casting time or duration and the strength of a spell is not perfect. The addition of spell power effects may change the mana efficiency of a spell significantly. When ordering the mana efficiency of your damage and healing spells, you should consider the effects of spell power, as this may change their ranking compared to if you used only the base states of your spells.

There are 5 categories of spells used to calculate spell power coefficients: direct (instant-effect), over time, hybrid (has both a direct and an over time component), channeled, and area of effect. Some spells may belong to more than one category. For instance, channeled spells always act over time; area of effect (AoE) spells may be direct spells, or may be channeled over time. In general, the order of priority is: area of effect > channeled > hybrid > [direct | over time]. That is, a spell which is a channeled area of effect should be calculated as an AoE spell, rather than as channeled.

The coefficient can be determined by following some basic rules that are outlined in this section. It should be noted, however, that there are a number of exceptions to these rules, and that the true spell coefficient should be verified experimentally.

As of Patch 3.0.2, it is necessary to multiply the results of the standard equations by a factor of approximately 1.88 for all healing spells. This is a proportionality constant introduced to account for the fact that bonus healing behaved differently from bonus spell damage prior to the patch, and took on a different range of values.

Direct (instant-effect) spells
Direct spells are spells that apply all the damage or healing at one time. That is, they have an instant duration. The amount of bonus damage or bonus healing depends on the cast time of the spell before any talents or abilities are applied to them. Spells with a cast time of less than 1.5 sec or greater than 7.0 sec are treated as having a cast time of 1.5 sec and 7.0 sec, respectively.

Direct Damage spells:

C = Cast Time / 3.5

Direct Heal spells:

C = (Cast Time / 3.5) * 1.88

Table of coefficients

Example calculation using Rank 11 (L80) of Fire Blast (Mage):

Cast Time = 0.0 (treated as 1.5) C = 1.5 / 3.5 = 42.86%

Examples of such spells include: Healing Touch (Druid), Greater Heal (Priest), Shadow Bolt (Warlock)

Some exceptions of this rule are:
 * Soul Fire (Warlock) - 115%
 * Pyroblast direct damage: 115%, damage over time: 5%

Over time spells
Over time spells apply healing or damage over a period of time in ticks. The spell power coefficient depends on the duration of the over time effect.

Damage spells:

C = Duration / 15

Healing spells:

C = (Duration / 15) * 1.88

This coefficient applies to the entire duration of the spell. With a few exceptions, each tick receives an equal bonus. Therefore, the per-tick coefficient can be found by dividing the overall coefficient value by the number of ticks.

Prior to patch 2.0.1, there was a 100% cap on over time spells longer than 15 seconds. This cap has since been removed. There is no minimum duration cap for over time spells.

Table of coefficients

Example calculation using Rank 15 (L80) of Rejuvenation (Druid):

Duration = 15 Number of Ticks = 5 CTotal = 15 / 15 * 1.88 = 188.00% CTick = CTotal / 5 = 37.60% per tick

Examples of these spells include: Rejuvenation (Druid), Renew (Priest)

Some exceptions to this rule are:
 * Shadow Word: Pain (Priest) - 110%, increased beyond 140% with Improved Shadow Word: Pain, which extends its duration to 24 sec.
 * Curse of Agony (Warlock) - 120%.
 * Curse of Doom (Warlock) - 200%.

Hybrid spells (Combined standard and over-time spells)
The bonus for spells that have both a direct and an over time component is divided between these components. Currently, the equations are unknown for hybrid healing spells. Several equations have been proposed, but none of them provide correct results for all (or most) hybrid spells. Because there are so few hybrid healing spells, it may be the case that their coefficients are not set by equations at all, but are chosen directly by the developers.

For hybrid damage spells, the equations are:

x = Duration / 15 y = Cast Time / 3.5 CDoT = x2 / (x + y) CDD = y2 / (x + y) CTotal = CDoT + CDD

Example calculation using the Rank 14 (L80) Moonfire (Druid) spell:

Duration = 12.0 sec Cast Time = instant (treated as 1.5 sec) x = 12.0 / 15.0 = 0.8000 y = 1.5 / 3.5 = ~0.4286 CDot = 0.80002 / (0.8000 + 0.4286) = 0.6400 / 1.2286   = 52.09% CDD = 0.42862 / (0.8000 + 0.4286) = 0.1837 / 1.2286   = 14.95%

So the DoT portion of Moonfire (4 ticks) has a coefficient of 52.09% (~13.02% per tick). The DD portion has a coefficient of 14.95%. The total coefficient is 52.09% + 14.95% = 67.04%. This agrees very closely with the empirical values of 52% and 15%, respectively.

Examples of these spells include: Moonfire (Druid)

Exceptions to this rule include
 * Immolate (Warlock) - 20% (DD), 20% (DoT) (Hotfixed as of patch 3.0)
 * Holy Fire (Priest) - 57.5% (DD), 18.5% (DoT) (As of patch 3.0)
 * Regrowth (Druid) - ~30% (DH), 70% (HoT)

Channeled spells
Channeled spells, like over time spells, have their benefit distributed over the entire duration of the spell. It is split evenly over each tick assuming that each tick causes the same amount of damage/healing. The duration of the spell cast time is used to calculate the total coefficient:

For damage spells:

CTotal = Duration / 3.5

For healing spells:

CTotal = (Duration / 3.5) * 1.88

For both:

CTick = CTotal / Number of Ticks

Example calculation using Rank 13 (L79) of Arcane Missiles (Mage):

Duration = 5.0 Number of Ticks = 5 CTotal = 5 / 3.5 = 142.86% CTick = CTotal / 5 = 28.57%

Examples of these spells include: Hurricane (Druid), Arcane Missiles (Mage), Hellfire (Warlock). An exception to this rule is:
 * Drain Soul (Warlock) - 214.3%.

Area of effect spells
Area of Effect spells receive only 1/2 of the total bonus that they would if they were single-target spells. As with a direct spell, the cast time is used to calculate the coefficient. The 1.5 second minimum and 7.0 second maximum apply to area of effect spells.

Damage spells:

C = Cast Time / 7

Healing spells:

C = (Cast Time / 7) * 1.88

Table of coefficients

Example calculation using Rank 7 (L80) of Circle of Healing (Priest)

Cast Time = instant (treated as 1.5) C = (1.5 / 7) * 1.88 = 40.29%

Examples of these spells include: Arcane Explosion (Mage), Prayer of Healing (Priest), Circle of Healing (Priest)

In the Burning Crusade and patch 2.0 there is a diminishing return against multiple targets. That is, as the number of targets your spells affect increases, the less damage you will deal to them. The numbers for this mechanic aren't yet known.

Paladin special attacks
Some paladin abilities work different ways. Here are some formulas tested in the Beta version of the Burning Crusade.

Holy Shield, Retribution Aura (paladin) reflects damage:

5% of +spell damage effect = +damage applied for each charge

Only paladin aura benefit from +dmg.

Seal of Righteousness, which applies Holy damage on each melee attack:

One-handed weapons:

9.2% * Weapon Speed in seconds = Total 1.0 sec = 9.2% 2.2 sec = 20% Two-handed weapons:

10.8% * Weapon Speed in seconds = Total 2.6 sec = 28% 3.7 sec = 40%

Rules for applying spell damage and healing

 * 1) Calculate spell time using the base spell cast time before talents and gear. (The in-game tool tip will include those bonuses; refer to Wowpedia's spells section for base cast times for all spells.)
 * 2) Spells that take longer than 7.0 seconds to cast are treated as if their casting time was 7.0 seconds, and spells faster than 1.5 sec are treated as if their casting time was 1.5 seconds.
 * 3) Damage benefits are applied before any talents or buffs that may otherwise increase your spell damage.

Spells learned before level 20
Many spells have multiple ranks. To avoid abuse of lower ranks to have a similar effect at a negligible mana cost, any spell learned below level 20 receives a large penalty. If such a spell has a shorter cast time than a higher rank, this is also taken in to account. This penalty can be calculated by subtracting 3.75% for each level lower than 20.

(20 - Level Spell is Learned) * .0375 = Penalty

Downranked spells
The ability to downrank has been removed with the release of patch 4.0.1

Downranking, the act of purposefuly using a lower-rank cheaper spell, no longer has any mana benefit as of Patch 3.0.

Spells with additional effects
Spells with additional effects, like a slowing effect, receive a penalty for each effect. Typically the penalty is 5% per additional effect, but can vary according to the developers' whims. For instance, here is the calculation for Rank 7 (L80) of Insect Swarm (Druid), which is an over time spell with a chance-to-hit debuff:

C = (12.0 / 15.0) * 0.95 = 76.00%

Examples of these spells include: Blast Wave (Mage), Blizzard (Mage), Insect Swarm (Druid)

Spells that both damage and heal
Some spells, namely Life Drains, both damage the target and heal the caster. The bonus is split between the healing and damaging portion, roughly in proportion to the amount of healing and damage involved. That is, if a spell heals 4 points for every 1 point of damage, 1/5 of the spell's bonus will go to damage and roughly 4/5 will go to healing. Because bonus healing does not apply to these spells, the 1.88 multiplier is not used for the healing portion.

Thus Drain Life's bonus is applied 50%/50% to damage/healing, while Devouring Plague's bonus is split roughly 75%/25%. The exact equations are unknown at this time, but a reasonably close answer can be obtained by:

CDamage = CTotal / (Damage Amount / [Damage Amount + Healing Amount]) CHealing = CTotal / (Healing Amount / [Damage Amount + Healing Amount])

Examples of these spells include: Devouring Plague (Priest), Holy Nova (Priest), Drain Life (Warlock)

Exceptions

 * Corruption (93%), Curse of Agony (120%), Curse of Doom (200%) and Shadow Word: Pain (110%) receive a reduced bonus.
 * Drain Soul has its bonus reduced to half (214%).
 * Fireball has a small damage over time component, but is not considered a hybrid spell, so it receives only the Direct Damage bonus to its direct damage component. Spell damage gear never increases the DoT on fireball.
 * Holy Fire does not follow hybrid spell rules and receives 85.71% (DD) and 16.5% (DoT).
 * Mind Flay does not follow channeling rules and uses 57% damage applied.
 * Soul Fire is capped at 115%.
 * Pyroblast deals 115% of +spell damage on impact and 20% of +spell damage to its DoT component.

Additional notes

 * 1) +Healing does not apply to bandages or potions. Trinkets should no longer be affected.
 * 2) Shaman totems receive benefit from +Damage.
 * 3) Hunter Traps don't receive a benefit from increased spell damage.