+Spell damage vs +Chance to Crit Items

[bobby]

The thing i been wondering for a very long time now but never got into calculating

"increases damage and healing done by magical spells and effects by up to xx".

How much of the above do you need on a item so that that attribute is worth the same as:
"improves your chance to get a critical strike with spells by 1%"

This being on a frost mage with a 18 arcane / 33 frost talent spec.

From what i know to get the full effect of the by up to xx you need a spell with a 3 seconds or more cast time and instant cast spells count as 1 second cast spells.

I know this can be hard to calculate and take into account all spells so if ya take one spell take frostbolt as i cast that the most.

If anyone good at math can calculate this it be nice :)

[Wogan]

A good rule of thumb is 1% to crit increases your damage by 1% (for a frost mage, a bit more for fire mages because ignite stacks).

Frostbolt does roughly 450 damage at it's highest rank, so to increase DPS by 1% you would need 45/.857 = 53 +frost damage. (Frostbolt is only a 3 second cast, so recieves only 0.857 of your bonus.)

The more +spell damage items you have, the better %crit items get relative to more +spell damage.

[Bob the Beholder]

The direct math, I don't know. But I do know from my magely experience that, overall, with a frost build, +damage is more effective. Without the base increase of Critical Mass, getting a high crit chance off of intllect and equipment alone is very, very difficult to do. And when you get it, with frostbolt's already low damage, you'll be seeing frostbolt crits--even with Ice Shards--lower than untalented fireball crits (though faster).

Furthermore, if you pick up shatter, you can trigger a pair of crits pretty much anytime you want (with a little bit of luck) by opening with a frost nova and laying down a frostbolt/cone of cold combo. So why bother increasing the frequency of crits as opposed to their power, when you've already got a way to increase the frequency beyond anything you could get with equipment?

[Warlock]

It's hard to say a specific single number since the more of either you have the better the other one is.

On my warlock I rule-of-thumb 1% crit as being as valuable on an item as +10 damage because it's close enough to use as a basis for comparison and is easy to do in my head.

My normal shadowbolts average about 700 points each with my current set of +damage gear; crits add about 700 directly (Ruin) and potentially 560 indirectly (four Improved Shadowbolt charges each adding 20% to another shadowbolt). If I count half of the indirect buff (to allow for things like the mob dying, the debuff getting pushed off, the debuff pushing CoS off and DoT ticks absorbing the charges) that works out to just under 1000 damage per extra crit overall or +10 damage per 1% crit chance.

10 points of +damage gear gives +8.3 base damage to each shadowbolt. Allowing for a 15% crit rate with crits doing 240% total damage (Ruin and ISB again) boosts this to 10.04 - very close to the benefit of 1% crit.

This ratio (1% crit = +10 damage) can be easily argued in either direction - for instance it doesn't allow for the benefit +crit gives to fire spells or the benefit +damage gives to DoTs. It's good enough for my use.

The ratio for a frost mage should be similar but I don't know that tree well enough to do math for it. Are there crit-dependent talents in the tree that require judgment calls about how valuable the secondary effects of criticals are?

[Skandranon]

A good rule of thumb is 1% to crit increases your damage by 1% (for a frost mage, a bit more for fire mages because ignite stacks).

Frostbolt does roughly 450 damage at it's highest rank, so to increase DPS by 1% you would need 45/.857 = 53 +frost damage. (Frostbolt is only a 3 second cast, so recieves only 0.857 of your bonus.)
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Wogan, this calculation is to raise average damage by ten percent, not one. 1% crit is not equal to +53 frost damage.

[Wogan]

Haha wups. I thought that looked dodgy when I was doing it, but didn't pick that up. Yeah. So more like +10 damage then, as Warlock suggests.

[Tommi]

+dmg is very effective for spells that have low initial damage and relatively long casting time, but which are improved through talents. +dmg has less effect for spells that have relatively high initial damage. Thus, the effect of +dmg varies from spell to spell. In fact, it is very useful for low level spells, while being relatively less useful for high level spells.

This is the problem, when game designers use straight +damage modifiers, instead of % modifiers, such ED% in D2.

[Xanthix]

A good rule of thumb is 1% to crit increases your damage by 1%
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I thought that a 1% increased chance to crit would increase your overall damage by 0.5%, because a spell crit by default results in 150% damage, unlike a melee crit which is 200% damage.

Of course, there are various talent points to increase spell crits to 200% or even 250% damage. I don't know if that's what you were talking about.

[Tharn]

Most of the time you want to really consider 1% crit = 1% damage increase, because pretty much everyone puts points into Ice Shards or Ignite.

Finding a balance a quite tricky, since it depends on damage you already have. For example on Frostbolt, which gets ~86% of the spelldamage bonus:

450 dmg Frostbolt = 450/100 / .86 = +5.3 dmg = 1% spellcrit
600 dmg Frostbolt = 600/100 / .86 = +7.0 dmg
750 dmg Frostbolt = 750/100 / .86 = +8.7 dmg

So the higher damage you already have, the more valuable spellcrit is. But if you look at most items, the +dmg ones usually have more than +10 dmg and thus beat the crit ones typically having +1% spellcrit.

For fire mages this can be even trickier though, due to Ignite stacking. Since I never played fire mage for long enough, I can't comment on that.