*waves*
Soooo, I read a few posts about people claiming that dual casting does nothing but costs more magicka... so I figured, why not test that.

I am NOT trying to pin down the exact numbers, though I will show the ones I find, I just want to show that dual casting does indeed have an effect.
Then people cast start to argue about if it is a good enough effect o_O


I used conjurations and shock spells. The burning effect from fire complicates things, that is why I don't use it.

Conjuration single cast: 120s duration, 59 mana
Conjuration dual cast: 264s duration, 164mana

Magicka x 2.78
Effect x 2.2

So, longer duration, but effectiveness goes down quite a bit. Over time, there is a 25%-ish increase.

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Now, why not cast shock spells on that very conjuration? O_o

It took 8 single casts to kill it (did it several times).
It took 3 dual casts + 1 single to finish of the last sliver of life. (Again, several times.)

Mana cost was: 15 for single and 40 for dual which is a 2.67 ratio which is not the same as for conjuration. ( The ratio should hold regardless of skill/items if it was the same for all schools )

Which makes the total:
8x15 =120
3*40+15=135

So we gain in speed (it is a LOT faster to kill with dual cast) and loose somewhat in efficiency.
How much, exactly, is hard to tell, since the last single cast was overkill by a fair margin. But they do not end up being the same, since that last cast was needed every time.

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Feel free to point out any errors I have made. =)

Helpful, thanks

Disappointingly though it appears that the Magicka regeneration bonuses don't work when in combat

Has anyone else found this? If it's correct I think that's a huge error

You forgot the fact that a dual-casted shock spell with the right perk staggers the enemy and makes killing all but some story-boss monster easy as hell.

thanks for this, its enough to convince me

Yeah, it's an epic perk that. Makes a huge difference

The problem is that it's NOT really any faster than dual casting without the perk.

With destruction for example, if you don't take the perk, you can still dual cast for nearly the same damage and burn a lot less mana. The cost is not worth the pay off.

Which had nothing to do with this, since it is a separate perk. The question raised on the forums was if dual casting was nothing but a magicka drain.
Your point was indeed raised in defense of dual casting in other threads, but if that was indeed all dual casting did, then stagger would in effect cost 2 perk points rather than one.

Nearly the same damage:
I wanted to avoid this, since the numbers are a bit vague, but: 4 casts (double) compared to 3 and a fraction (dual): since there was just a sliver of health left after 3 casts, so lets say 28-30% increase in damage), this is not correctly shown in the numbers above since there is no such thing as a fraction of a cast.

Mana cost when comparing double cast (perkless) and dual cast is +38%.

So, an damage increases 28-30%, and we can see that the mana efficiency does get worse, but not as much as your wording would imply.

I make claims my numbers lack precision to support, but since you started it, I feel you can't really be the one to throw stones

EDIT: My wife was talking to me as I wrote and that apparently shut down my brain O_o

It seems to me, from looking at the numbers posted by timeam, that the answer is obvious. Dual casting burns more mana but finishes an enemy off quicker. Simple enough really

So, basically a dual cast spell does more damage,or two spells cast at once? I'm confused

Dual cast does more damage, I think

I saw a thread about this yesterday (not sure where it went... didn't feel like searching) so I decided to find out for myself and did some testing last night!

My total mana pool was about 480. I had on Marokei Mask, and some other mana regen type items (arch mages robe, etc..). So I found a dungeon and a ranged archer that I could simply hide around the corner from and he's never come into view to I had my testing grounds. It was a little crude, but basically, I cast stone skin enough times to deplete my mana, could never get it fully empty but got to about 8-10 mana average. I waited for it to refill which took right about 30 seconds. I then took the mask off (which for those unaware grants +100% mana regen) and cast until empty. This time it took about 50 seconds for it to refill. Even the first time I cast and was waiting for it to refill I could tell it was going to take longer. Mana regen bonuses definately work in combat, but they scale like non other. oh and I think it takes roughly 7-9 seconds for my mana pool to refil outside of combat, I never did take my mask off to test the difference outside of combat. I only tested this a couple of times, but it was more than enough times to tell there was a difference.

TL;DR :

Crude test done.
Took roughly 30 seconds to 480 mana pool to refil after depleted.
Took off Marokei (+100% mana regen), took roughly 50 seconds for mana pool to refil after depleted.
Takes roughly 7-9 seconds for mana pool to refil outside of combat.

Dual casting is VERY important for illusionists.

Illusion spells are all or nothing - if the enemy is too high level the spell won't take. Dual casting increases the effective level of the spell allowing you to cast illusions on higher level foes that are otherwise unaffected

Dual cast does more damage. It is the mana ratio that is supect =)

dualcasting is garbage for destruction. the stagger perk doesn't work on the most handy spells.

I guess with all the nitpicking, I have to devise a more precise test, I need something with a ton of hitpoints that won't kill me if I stand still and aim carefully...