Tuesday, November 8, 2011

2d6 Versus 1d12 and Clerics Turning Undead

A discussion of clerics turning undead got me thinking about how likely they would be successful given multiple attempts.  To turn undead, you roll 2d6 and compare the result to the target.  I wanted to see how likely one was to succeed against varying hit-dice of baddies, and what the cumulative probability would be if there was no limit on the number of attempts. That in turn got me thinking about why we use 2d6 instead of 1d12 and what the impact would be. 

The d12 is probably the least loved die.  People tend to use 2d6 instead.  But should they? 

The answer is, of course, it depends on what you want to do.  The reason is that the results are distributed differently. 

Figure 1:  1d12 results are uniformly distributed while 2d6 follow a peaked distribution favoring moderate outcomes.

Using 2d6 tends to force more moderate outcomes at the expense of more extreme outcomes.  Using 1d12, since the results are uniformly distributed if the die is fair, will result in more extremes.

Figure 2:  2d6 makes exceeding higher targets less likely while lower targets are easier.
Using 2d6 makes clerics more powerful against lesser undead with lower target numbers to turn, but less powerful against more powerful undead with higher targets.  Using 1d12 makes them more powerful against powerful undead and less powerful against easier undead.  It's an interesting result, I think.


  1. Assuming you are striving for consistency within your campaign setting (i.e. not changing the dice you use halfway through a character's career) it would seem most folks would want to stick to 2D6, as level progression brings that target number down over time...you may have a better "straight" chance of turning high level undead at one level, but progression is "always upward" in D&D...you will eventually bring that target number down to 7 or less.

    Sorry, D12. *I* like you.
    : )

    1. My purpose wasn't to advocate one position or another, merely to explain the trade offs in response to a discussion I'd heard elsewhere. You're right, I didn't think about how the choice of 2d6 v. 1d12 affects the power of clerics as they advance. At first glance it seems that as their targets fall for a given type of undead clerics are more powerful under 2d6 than with 1d12.