In my study to truly understand the relationship between AC and DR, I decided empirical results are the only true good ones. And since I did all this work, I thought I'd share the results for anyone who cares.
So what I did is go through all of the MMI. For every creature CR 1/4 through 5, I recorded each damage it could do on its full attack as a data point. So creatures with 3 attacks got 3 data points. The results are scewed in that I had no correlation for commonality among creatures (for example goblins encountered more frequently than rasts for example) but as a 1st approximation I think its pretty good. This data does not include crit data, but as most monsters only crit on a 20 it shouldn't alter things a great deal.
This results also includes a few monsters from Arcana Evolved, and I did not include skeletons, zombies, and dragons (dragons are from Arcana Evolved).
With 438 datapoints tabulated, the average damage over this CR range is 6.38. That means that within that CR range, that's the general damage you will take every time you get hit.
With that average in mind, I now know that DR 1/- is equivalent to +1.648 AC.
And knowing is half the battle.
So what I did is go through all of the MMI. For every creature CR 1/4 through 5, I recorded each damage it could do on its full attack as a data point. So creatures with 3 attacks got 3 data points. The results are scewed in that I had no correlation for commonality among creatures (for example goblins encountered more frequently than rasts for example) but as a 1st approximation I think its pretty good. This data does not include crit data, but as most monsters only crit on a 20 it shouldn't alter things a great deal.
This results also includes a few monsters from Arcana Evolved, and I did not include skeletons, zombies, and dragons (dragons are from Arcana Evolved).
With 438 datapoints tabulated, the average damage over this CR range is 6.38. That means that within that CR range, that's the general damage you will take every time you get hit.
With that average in mind, I now know that DR 1/- is equivalent to +1.648 AC.
And knowing is half the battle.