This is my understanding of how damage works, how it interacts with spells, intelligence, +damage, elemental damage, etc.
Unlike in D2, a wizard cares deeply about his weapon. It isn't just a “stat stick” with bonuses on it. No longer are casters fairly equipment independent.
All offensive skills have their damage based on the weapon you have equipped. For example Magic Missle does 110% of your weapon damage, as arcane damage.
Weapon damage is used for spell damage. And weapon attack speed factors into your casting speed. Faster weapons cast faster too.
How does Damage Work?
----------Base Damage--------
Lets take a look at Magic Missile, and a wand (weapon or axe) with a 8-12 damage range, once per second, this results in an average 10 DPS. This is what your weapon reports as DPS, the other stats are there, but in the small print.
The weapon damage is the actual damage the weapon has, not DPS. This is why 2 hand weapons are often favored. They do more damage, but slower. So they may do 15 damage, but only 0.65 times per second. That’s still 10 DPS. But the spell amplifies the damage more, as it starts with more.
+damage items, such as rings, increase this base damage. This is a key factor to increasing your total damage output, as it gets magnified by all other damage multipliers (spells, int, skills).
----Intelligence Bonus -------
The intelligence percentage works like this. Each point of intelligence boosts damage by 1%. So 110 int, increases damage by 110%. That is a 2.1 multiplier (shifting it from % to decimals, and treating it as a 100% increase)
--Spell Bonus--
Magic Missile then comes into effect, and deals damage specified it by its spell effect, listed as 110% under the skill. So it takes the damage listed in your inventory screen, and does 110%. If you did 100 damage, MM will hit for 110 damage.
Guide continued after the page break..
--Putting it all together--
To determine the spell damage you take your:
(Weapon Damage with +damage from items) * Intelligence % * Spell Effect
So, if we start with a wand that averages 10 damage we get:
Weapon Damage (10) * Intelligence (2.10) * Spell Effect (1.10) for: 23.1 damage.
Now, if you increase the weapon damage, the effect grows. Not only does the weapon provide a bigger base damage to start with, but the % increase from intelligence and the spell have a bigger impact. 10% of 15, is larger than 10% of 10 for example.
So if we use a weapon that does 15 damage (the extra 5 damage from the weapon, or +damage items) we get:
15*2.1*1.1 = ~34.6 Damage.
That 5 additional damage gave us a head start, but the int and spell effect also gave us ~19.6 damage from intelligence and spell effect, while the 10 damage weapon only gained us 13.1 from our base.
This means, especially at low levels, that an increase in weapon damage, either from the weapon, or +damage rings etc, can have a huge effect on your damage output. That +damage is added to your base weapon damage, so it’s also amplified by your intelligence and your spell effects. If you have to choose between +damage or +int, go for the damage.
At higher levels, when adding 5 or 6 damage to your base isn’t that big an increase the need to prefer damage over intelligence boosts evens out a lot more.
The short version of this is that the damage reported on your inventory screen is the damage the skills boost when you cast them. If you get that number up, through whatever combination of items, your spell damage will go up. It factors in all items and modifiers before the spell automatically.
The damage increase listed when comparing items
The damage increase listed in the stat summary of the items, when you compare them, is accurate, as best as I can determine. If it says your damage will increase 10 points by swapping the items, it appears accurate when I test by monitoring Hydra damage.
There is only one catch. For the time being, when comparing a 2H weapon to a 1H weapon, the game only reports the damage increase from swapping the weapons only. It does not factor in the loss of any bonuses from your offhand item. After you swap out a 1H item for a 2H, check the inventory screen for the final result, listed on the left side of the inventory window. When comparing a 1h to a 1h or a 2h to a 2h, the item reports the correct change in stats.
Elemental or Bonus Damage on a weapon:
So you have a 10dps sword, with +2 cold damage…why don’t you strike for 12 damage?
--The damage listed on the weapon is already integrated into the weapons base damage. The DPS takes it into account. You can confirm this by socketing a Ruby into your weapon.
The base damage jumps, AND it lists the rubies bonus…so it does the math for you, but lets you know in case you have any +Cold damage % skills, which will only effect the +2 cold damage (not the entire weapon damage).
--The spells you cast usually replace the elemental damage type with their own. +2 cold damage from a physical blow will chill or freeze an enemy. From Magic missile, it’s converted to arcane, and will not chill your target. The damage is still there, in the base damage. It just isn’t cold damage anymore. Some spells retain the damage type. Spectral blades IIRC will deal cold damage if using a cold weapon.
2H vs 1H weapons
Now, does this mean that bigger base damage (i.e. 2H weapons) are always better than 1H? First, that’s gear dependent. If you get a nice off hand item you may end up doing more damage if you factor in it’s bonuses. Second you give up any other perks the off hand item provides. So no blocking from shields, less magical abilities (only one items worth in the 2H, vs the two items worth in the 1h & offhand). That can factor into decisions.
Weapon Speed
Wizards still care about this, as many spells casting time is linked to the weapon speed. If you have a faster weapon you can cast more spells per second. This is really good if you rely on signature (free) spells, or have abilities that you want to trigger. This, btw, is often refered to as a "proc" for programmed random occurance. For example the lightning rune on magic weapon can trigger extra lightning strikes. Faster casts mean more chances for it to proc. (Thanks Leetnoob)
However if you like big burst damage spells (arcane orb) you may just want more damage. The limiting factor for them is not how fast you can cast them, but that you can only cast 3 or so before you are out of AP. Some spells, like Hydra, are extreme examples. You only get 1 hydra….doesn’t matter how fast you cast it, so more damage outweighs faster weapons, so 2H weapons win there. (Thanks Morphos)
For channeled spells (rays and torrent) the 2H weapons can still out perform faster 1H weapons, and this comes down, again, to mana cost. The two weapon types will have similar DPS, but the 1H weapons trigger more often (as seen by a "pulse" in the beams), draining AP more often. So you spend more AP per damage point, for the same DPS. Unless you have some abilities you want to proc, this may be to inefficient for some builds & gear sets. (Thanks Dedna & JumpSec)
This doesn't mean 1H weapons (with a good offhand) are automatically worse. It is possible to make up for the AP "inefficiency" of 1H weapons. Faster casting essentially costs more AP per second, meaning a fast caster will be out of AP and have to wait for the recharge. The advantage of the 1H is that they won't just wait during this phase. A skilled player will spam the "free" signature spells during this time. This may be enough to close the damage gap between the weak AP spells of faster casts, compared to the strong AP spells of slow casts.
It can also be argued that it allows more flexibility and control. A fast caster will throw out 3 weaker Arcane Orbs (AO) really fast to smash the front ranks of a crowd, then fire off some chain lightning to catch stragglers, or try to get the back ranks (where summoners like to hide). If you throw in some other abilities triggered on each hit (paralysis, AP on crit) you may make up for the AP inefficiency in other ways (signature spells runed for AP gain)
Whether or not it's worth the extra work is up to the user, the available gear and their playstyle.
Damage Boosting Skills (MAGIC WEAPON)
Magic Weapon boosts your weapon damage, which increases spell damage. This bonus is applied alongside the intelligence and spell effect boosts. So a 10% boost from magic weapon on a 100 damage item, makes it a 110 damage item. If you have a 200% intelligence boost, and spell effect (to make the math easy) that gives you 440 damage output. Without the magic weapon, you would get 400 damage.
Note: Magic weapon may be bugged, and providing a 20% damage boost instead of the 10% reported on the skill.
These skills all stack, so if you get 10% from MW, 20% from the slow time rune, those both multiply your base damage. So the 100 damage item is run through:
100 damage * 2 (200% intelligence) * 2(spell effect %) * 1.1 (10% MW) *1.2 (slow time rune) = 528 damage
Some skills, like Familiar, do not boost the damage, as they fire their own bolt of energy at your target. The end effect is the enemy takes more damage (at the 20% familiar reports) it’s just not from your arcane orb, or other spells. That is unless you select a specific rune.
