# Diablo 3 RoS Damage model

Benchmarking and dmg-prediction gear/spec in D3 is quite difficult... my question is in this "field"...

I would like to know how the damage model works regarding the "+ Holy/Fire/Lightning %dmg" and the "+ X% (skill name here) dmg"... consider the following scenario: I have a char that casts a fireball (fire dmg) and it hits for 100 dmg. so, consider `Ring A` a ring that only has 1 stat and that stat is + 10% fire dmg and `Ring B` gives + 15% fireball dmg

1. If I use Ring A (gives 10% fire dmg,) the fireball will hit for 110?
2. If I use Ring B (that gives 15% fireball dmg) the fireball will hit for 115?
3. If I use Ring A and B the fireball will hit for 110, 115, 125, 126.5?
4. If I crit for 2x, while using only Ring A the value of the hit will be `(100*2)+10%`(220) or `(100*2)+(10%*2)`(240)?
• I don't know for sure, so this is going in the comments. Scenario 1 and 2 are correct. Scenario 3 I believe would be 125 as I think +skill damage is added together. Critting for 2x SHOULD be 250 because you take the base (125) and then multiply by 2. The only times where the values multiply differently I think is when you have +Elite damage, skill/elemental damage, and % damage debuffs (Mantra of Conviction for instance). Once again, I could be wrong about how the damage sources are added/multiplied together. Commented Jun 18, 2014 at 20:29
– l I
Commented Jun 18, 2014 at 20:39

Here's what I know from testing and reading the Diablo 3 forums: there are several groups of buffs and each group is multiplicative with the other groups (and thus a separate multiplier). Check out this thread for more information on multipliers.

1. The `+10% fire damage` from `Ring A` falls in Class B
2. The `+15% fireball damage` from `Ring B` falls in Class A3.
Assuming you're only wearing `Ring A`, then your 100 damage fireball with Fire element will hit for 100 * 1.1 = 110 damage.
Assuming you're only wearing `Ring B`, then your 100 damage fireball, regardless of element, will hit for 100 * 1.15 = 115 damage.
Assuming you're only wearing `Ring A` and `Ring B` and no other modifiying equipment, then your 100 damage fireball with Fire element will hit for 100 * 1.1 * 1.15 = 126.5 damage, which will be rounded to 127.