Re: Converting D&D DC to GURPS Skill penalties
 

Good point, I forgot about the 3- rule. But the possibility of allways-win or allways-loose situations is precisely my critique on the system.

I agree that it can be converted nicely, I just don't think they way to go is by direct mathematical formulas converting DC to bonus/penalties. Or probability of success for that matter. It's way better to look at it from the descriptive/subjective perspective... you'll end up with more satisfying results in GURPS, instead of imported success rates that don't "feel right".

Re: Converting D&D DC to GURPS Skill penalties
 

Actually GURPS and D&D have similar concepts here. B345 says: "You may not attempt a success roll is your effective skill is less than 3.". The only exeption to this is defence rolls that always succeed on a 3-4.

So if modifiers take you below 3, no roll, similar to the DC being too high.

Not the same. Similar.

An example would be an average-bloke-untrained-pistol-shooter trying to hit something at 100 yds. Even with aiming.

Re: Converting D&D DC to GURPS Skill penalties
 

Sorry to Necro this thread, but I have actually worked out this problem.

First Average for d20 is 10, and average for Gurps is 0, since Gurps uses a "penalty shift" system.
And the average "default" penalty in Gurps is 5, which I think goes right in line with setting the base-case for Gurps at a DC 15. Which was arrived at by totally different means in the first post.

Now to get the mechanical conversion, you have to figure out the relative value of a +1, which you can figure by comparing the deviations from the means of the two systems. In the case of Gurps you have a deviation of 2.96, and in the case of d20 the deviation is 5.77. That means that you are close to a 2 to 1 value for each +1.

That means the following would more or less be equivalent penalties to DC's:

5 - +7
10 - +4
15 - 0
20 - -4
25 - -7
30 - -11
35 - -14
40 - -18

That being said, I can't remember seeing a penalty above 10 in Gurps. Gurps seems to max out at an (mechanical) equivalent of DC-30.

Re: Converting D&D DC to GURPS Skill penalties
 

Bwahahahaha. Hang on while I find the thread. *shuffles around in the back archives*

Here it is. Absurdly High Skill Levels

Re: Converting D&D DC to GURPS Skill penalties
 

Yeah. -10 is generally the single worst modifier you can have (and even that's not true: Range penalties can get worse than -10). But mods can stack. People often point to combat because they're familiar with that, but quite a few other things can have stacking mods. If you're using TL/8 surgery to stabilize a mortal wound on an elf (-2) who is at -4xHP (-4) while you have nothing but a butcher's knife and your fingers (Improvised tools at best -5, with -2 for a lack of anesthesia), on an unsanitized dining-room table (-3), and you only have 15 minutes (10% of time, -9), you're at -25.

(And that scenario might sound ridiculous, but I could actually picture an Urban Fantasy game where a severely wounded elven prince needs to be tended to by rushed, retired physician in the midst of a warzone. In fact, the scene in Walking Dead where the boy had been shot and a veterinarian needed to perform surgery on him in a bedroom with minimal tools, while a lesser version of the above, would have some pretty steep penalties too).

If you dig around enough, you can find similar penalties for other skills (Driving in near pitch-black darkness, with a damaged semi- when you've never driven this model AND you're used to TL 6 vehicles, while moving at top-speed and badly injured; investigating a murder scene in the midst of a busy street three days after the event, while drunk, with no tools except the Mk 1 eyeball, etc)

Re: Converting D&D DC to GURPS Skill penalties
 

I once started a thread on extreme penalties to skills and the feats that come with said penalties. I'd be happy to see more examples.

Re: Converting D&D DC to GURPS Skill penalties
 

I mean we can go there if you want...

Re: Converting D&D DC to GURPS Skill penalties
 

Just go with each 2 over 15 gives you a -1 in GURPS. It's close enough, and what I use for porting traps and stuff.