How much to power attack for?

[Commander_Vimes]

Does anyone have a good system for determining how much they should power attack for? Right now I am playing a combat Cleric with a Guisarme. With Divine Power up I have a BAB of 11 to use to power attack with (for a total mod of +19 on the first strike). Is there a set percentage that is generally best to power attack for?

[UglyPanda]

Use this:
http://donjon.bin.sh/d20/power/

Knowing how much to PA for requires a bit of metagaming, since it differs depending on AC.

[PhoenixRivers]

There's a formula to use, but it takes a while to factor out.

I'd need to know your damage per hit without power attack to calculate.

[kemmotar]

Take the shock trooper feat and never look back...otherwise, try to calculate how much AC the other would have (usually easy with the armor wearing types and arcane casters) and then try to be able to hit on a 10....that would be ideal, though difficult in most cases especially after power attack...

Count approximately what you need to roll to hit...10 should be average and then above that is risk calculation.

[Eldariel]

It depends on iteratives though. Generally later on with enough iteratives, you want to hit on 2 and PA any excess you have afterwards (more on Charges, of course). Run some numbers through the calculator. You'll get a hang of it soon enough.

Oh, if opponent has DR, the value of PA increases dramatically. Just something to keep in mind; it's really a factor of your base damage.

[Random832]

Use this:
http://donjon.bin.sh/d20/power/

Knowing how much to PA for requires a bit of metagaming, since it differs depending on AC.

ugh, that's not metagaming - the fact that PA itself uses a number means that you have to put "fighter's guess as to how good the enemy's armor is" in terms of a number, but the core concept of "fighter guesses how good the enemy's armor is and puts any fighting ability he doesn't need to score a hit into putting more damage" isn't metagaming.

[UglyPanda]

I said a bit, not a lot. I'm not one of those "Oh noes, you know dragons have low touch AC types!", I'm assuming that the OP isn't going to bring a laptop to the table, so he has to know what the ACs are way ahead of time if he uses that.

Edit:
Of course, he could go the OCD route and write out the best amount to PA for for each AC from 20 below to 20 above, put it on a sheet, and bring the sheet to the table.