A spell coefficient in classic WoW is the share of +spell damage or +healing a spell gets; it is cast time over 3.5 seconds, or duration over 15 for a DoT.
direct damage or heal: coefficient = cast time / 3.5 (cast time clamped to 1.5 … 7 s, so 0.4286 … 2.0)
instant cast: coefficient = 1.5 / 3.5 = 0.4286
damage over time: coefficient = duration / 15 (spread over the ticks)
channelled: coefficient = channel time / 3.5 (spread over the ticks)
area of effect: the above, halved
spell learned below level 20: × (1 − 0.0375 × (20 − spell level))
bonus from gear = +spell damage (or +healing) × coefficient
How much of your +damage or +healing a spell gets is set by its cast time, not by the spell: a 3.5-second cast gets all of it, an instant gets three sevenths, a DoT gets its duration over 15 seconds. A spell that is both direct and over time splits the bonus between the two parts under the same rule.
| Spell shape, with +300 spell damage | Coefficient | Bonus |
|---|---|---|
| 3.0-second direct damage cast | 3.0 / 3.5 = 0.857 | +257 |
| Instant direct damage | 0.4286 | +129 |
| 18-second DoT, 6 ticks | 18 / 15 = 1.2 | +360 in all, +60 per tick |
| 3.0-second AoE | 0.857 / 2 = 0.4286 | +129 to each target |
| 2.5-second cast, rank learned at level 12 | 0.714 × (1 − 0.0375 × 8) = 0.5 | +150 |
Last checked: unverified against Forever. These are the long-established values of the classic ruleset (the 1.x game of 2005-2006); World of Warcraft Forever is in beta and may differ. When you test this one in Forever, post your numbers in Theorycraft.