Converting D&D DC to GURPS Skill penalties
 

My gaming group, which can't meet as regularly as we'd like, has decided to do a series of one-shots from different systems. But then they decided that they'd rather stay with GURPS rules. So I'm picking up some published adventures from various systems and converting them over to GURPS.

Our first foray will be a D&D 3.5 dungeon crawl. (Dungeon Fantasy 1 & 2 came out just in the nick of time.) I'm not having trouble with the monsters, or any of the seriously crunchy conversion stuff. But I'm completely stumped on how to convert DC (difficulty class) to GURPS skill penalties. I want to do it with some semblance of mathematical accuracy rather than an arbitrary "DC 15 = easy and Skill-0 = easy." Unless that's truly accurate, of course.

It's one thing to talk about probabilities and die rolls... but DCs are open-ended. The die roll is added to skill ranks and attribute bonuses. Which presents a problem: in D&D the die roll is vastly more determinative than it is in GURPS. Say you have skill rank 1 in Open Locks. Before I started working this out I imagined this to be equal to, say, Lockpicking-DX in GURPS. But the average schmoe with Lockpicking willl have Lockpicking-10, the average schmoe with Open Locks will have Open Locks 1.

So I roll 3d6 vs. Lockpicking, and just under 50% of the time I will succeed against a crappy lock (no skill penalty). Same situation in D&D terms: crappy lock, say DC 15. 35% of the time I will succeed (because I only need a 14 or better, so 13 times out of 20 I will fail.)

But a simple DC 15 / GURPS no penalty lock is pretty much the only one that makes sense to me. Let's take it up to DC 25... that's a nice, moderately tough lock. Say skill penalty -6 in GURPS. Same skill rank/level. In GURPS I'd be rolling against Skill-DX-6, which for the average person would be 4. Possible... insanely hard, but possible.

Completely impossible for a D&D character with 1 skill rank. Can't "roll" higher than a 21. Needs at least 4 more skill ranks to make it at all doable. But DC 25 is a *common* difficulty for things like locks... it *assumes* characters will have skill ranks and modifiers totaling above 1.

So here's the question: what does that mean for GURPS? If a DC 25 lock *requires* at least a +5 modifier via ranks & attribute modifiers, what's the best way to translate that requirement over to GURPS skill level penalties? In GURPS terms you'd (grossly generalizing here) want to have enough skill to offset the penalty enough to make it a 50-50 shot (say, Lockpicking-16 or 17, to offset a -6). Should I therefore be looking at matching required skill ranks to required CP cost (to boost the skill to 50-50)?

Am I overthinking this? I'll bet I'm overthinking this.

Re: Converting D&D DC to GURPS Skill penalties
 

You're overthinking this.

Mainly, DC levels from D&D and skill penalties/bonuses in GURPS work differently. The assumptions on what's "easy" and what's "hard" are different.
In D&D you need to be quite competent to atempt something even mildly hard, while in GURPS you can try with just about any dificulty, although you're likely to fail if you're incompetent (and might get hurt in the process).

Also, I wouldn't call an easy, regular, run-of-the-mill lock a +0 difficulty. Remember, you use skill rolls at flat score under "adventurous and stressful situations". So I'd call a +0 lock "average" or "challenging". While, an easy lock would be at a bonus. And a hard lock at a penalty. Use the dificulty levels sugested in Basic, they clear this up quite a bit.

I wouldn't try to establish a paralel between the success rate. D&D tolerates much lower success rates and still calls people skilled. Honestly, If I can only lockpick an easy lock half the time I'm not that good a locksmith.

Re: Converting D&D DC to GURPS Skill penalties
 

I believe GURPS 4e skill rolls are 'heroic' by default (I am missing the nomenclature for this), though not Cinematic, versus 3e which was realistic by default. So mundane locks under normal circumstances are much easier perse than what the characters skill number represents. This may impact some of the DC conversion since D20 is traditionally 'cinematic' to 'heroic' only, specifically addressing the *requires* problem.

Also a crappy lock would give some sort of bonus to lockpicking I would think which skews the example flow I think.

For what its worth I think your on the money math wise, its just not clear to me if the D20 character and the GURPS characters are making the same basic rolls under normal conditions. If a GURPS 20 skill is legendary, then beating down DC ~30 seems solid.

I find this useful (the unified table)

http://www.fudgefactor.org/2005/10/c...-to-fudge.html

Re: Converting D&D DC to GURPS Skill penalties
 

I agree with Gudiomen.

It's much easier, and probably more accurate to simple make some estimation based on what seems right instead of going into math.

Personally I would simply give a +/-2 difficulty per DC:5, with DC:20=+0.
The reason I pick DC:20 as the default is because a typical D&D adventurer is about level 4-10. At the lower end you can have an effective skill of +10 if you have really focused in a skill, while at the upper end is its easy to have +10 in a secondary skill. At levels 6-7 most have +10 in a few of their class skills.

So:
DC:5 = +6 [even at default everyone could do it]
DC:10 = +4 [Everyone with just the most basis of training could do it]
DC:15 = +2 [And easy task for anyone with training, difficult for the untrained running on default]
DC:20 = +0 [Takes a skilled user to make it routinely, but anyone with training has a fair shot at it]
DC:25 = -2 [Difficult even for a skilled person]
DC:30 = -4 [Takes an expert and even he would have trouble]
DC:35 = -6 [Only the most skilled can do this and still they would have a higher chance of failure than success. Even the best of the best would not be guaranteed success]
...and so on.

IMO, this also fits pretty good if you compare the "Difficulty Class Examples" in the D&D DMG p.31, with the "Task Modifiers" in GURPS Basic p.345.

Re: Converting D&D DC to GURPS Skill penalties
 

The "back of the envelope" guideline I use with skill ranks is usually Skill Ranks = points in the skill, but that's really only a rough number and it's probably better just to keep in mind that someone with a really high effective skill in D&D should have a really high effective skill in GURPS too.

DCs, on the other hand, because of the differences in the dice system, probably can't be directly converted but there are guidelines you can work out.

At the low end things are roughly linear, but because D&D has a flat progression and GURPS has a bellcurve, I'd be wary of converting high DCs linearly...

a DC 5 is really hard to fail at. In GURPS and in D&D this kind of task usually isn't worth rolling for unless you're operating under a lot of situational penalties. Call it a +8 or even +10.

a DC 10 is something that someone with 10s in all his stats and completely untrained in has a 50/50 chance to succeed at. That's probably a +4ish to effective skill, offsetting a default penalty of -4.

a DC 15 is something someone with a slight aptitude (a 12 in the stat) and 4 skill ranks (a level one PC who's trained in it a bit) has a 50/50 chance to succeed at. I'd say roughly +2 to +0

DC 20 is hard for someone with a skill modifier of +5 - only a 25% chance of success. That's an effective skill of 8. A lightly trained person (skill 10-11) is looking at a -2 or -3, and skill 10 or 11 sounds about right for a 1st level character.

A character with +5 skill can only succeed at a DC 25 task if they roll a natural 20. 5% chance of success is roughly an effective skill of 5, so call it -5 to -6.

I suppose if you want a rough rule of thumb, every +5 DC roughly equals a -2 or -3 GURPS TDM...

but honestly, I think you'll be better served by looking at the described situation and just using the GURPS rules (possibly get your hands on a copy of Dungeon Fantasy 2, the first chapter is full of good dungeon delving stuff).

A basic house lock, by the way, is probably +5 to pick. Many folks will use this to offset a -3 to -5 in "time spent" penalties to jigger the lock really quickly. A skilled lock picker can open a basic house lock in about the time it takes for me to fumble for my key ring and open the door.

Re: Converting D&D DC to GURPS Skill penalties
 

Seems like we guestimated the same numbers :) Must mean they are right. I just doesn't like basing things on D&D level 1 characters because they are lowpowered compared even to a 50 pts mook. I think to have a fair comparison with a typical GURPS character, you need at least level 4.

Re: Converting D&D DC to GURPS Skill penalties
 

I'm not going to attempt to analyze it. Comparing DCs intended for a linear distribution (d20) to penalties intended for a bell curve (3d6) simply isn't going to work out nicely. In particular, the impact of modifiers will depend critically on where the chap rolling 3d6 happens to be on the skill curve.

But on that last point . . . I wouldn't assume skill 10. I think if you're even going to attempt an analysis, you should do something akin to "GURPS skill level = 12 + D&D skill ranks/5." Let's face it, in D&D, if somebody is going to bother will a skill starting out, he's going to make sure it's one that will be getting +1 to +3 to from an attribute at 12-16, or about +2 on average. That's like a score of 12 in GURPS. After that, it's hard to rate skill -- but since DC increases are generally given in 5-point chunks while GURPS tends to give great weight to each -1, 5:1 is as good as anything else.

Re: Converting D&D DC to GURPS Skill penalties
 

Go back and review the Basic Set p.345-346. A +0 is for "adventuring" tasks, ike "Driving roll in a high speed car chase" which is a lot harder than "pick average lock" or somthing. I really wish we had more examples of skills with their TDM, but all we have is driving. There was an attempt to start that on this board somewhere, but it faltered.

Re: Converting D&D DC to GURPS Skill penalties
 

Do note that many skills come with standard modifiers! Look for colored paragraphs like this:

Modifiers: Some modifiers.

Also, don't overlook the fact that there are several sets of standard TDMs for vast swaths of skills: Comprehension Levels (p. B24), Culture (p. B23), Equipment Modifiers (p. B345), Familiarity (p. B169), Geographical and Temporal Scope (p. B176), New Inventions (p. B473), Physiology Modifiers (p. B181), Tech-Level Modifiers (p. B168), and of course all the combat modifiers on pp. B547-550. The "generic" TDMs on pp. B345-346 are more "instead of" than "as well as," although you can certainly use them to fine-tune.

Re: Converting D&D DC to GURPS Skill penalties
 

For a simple answer in my campaign, I took this information from the table of the D20 SRD:

Difficulty (DC)
Very easy (0)
Easy (5)
Average (10)
Tough (15)
Challenging (20)
Formidable (25)
Heroic (30)
Nearly impossible (40)

And compared it the "Task Difficulty" column on page 345-346 of the Gurps Campaigns book. So, that worked out (roughly) for me to..

DC 0 = +6 or +7
DC 5 = +4 or +5
DC 10 = +0
DC 15 = -2 or -3
DC 20 =-4 or -5
DC 25 = -6 or -7
DC 30 = -8 or -9
DC 40 = -10

Adding a pinch of good judgement, it has worked for me for quite a while.

Re: Converting D&D DC to GURPS Skill penalties
 

D&D also uses "everything gets harder as you level" and "everything gets easier as you level" at the same time, so it gets wonky there, too

Re: Converting D&D DC to GURPS Skill penalties
 

Thanks for all the suggestions, I'm glad that the eyeballing "system" I'd worked out is basically what others came up with, too. I know that the two systems are quite incomparable (it's not just that d20 is linear, it's that the underlying theory behind what the roll is *doing* is completely different).

Re: Converting D&D DC to GURPS Skill penalties
 

Exactly, like Bruno pointed out, there are different underlying assumptions on the relative dificulty level, the time it takes to try something, etc...
The take 10 or take 20 options (I'm rusty in D&D never played it more than once or twice) are good examples of how mechanics work differently. In D&D taking more time can garantee sucess. And a mildly challenging task can become automatic if you're skilled enough. In GURPS, extra time will get you a bonus to your chances, and no matter how skilled you are, there's allways a possibility of failure.

The length of the turn alone can make a big difference, it turns GURPS Stench spell, into D&D Death Cloud (or something, like I said, it's not my native system).

There's also the genre differences, such as the assumed level of heroism and realism. The system's assumptions on what constitutes a decent rate of sucess. In GURPS, beggining characters can be very skilled at their knowledge and skill niches, in D&D they invariably suck (skill level limits).

Re: Converting D&D DC to GURPS Skill penalties
 

Yes, this is one of those things about which I had to make peace with myself in DF. Being a complete purist about old-school dungeon RPGs would have meant starting the PCs out at 75-100 points with numerous definitive skills in the 8-12 range. But being a complete purist required me to allow many abilities -- like being able to start out as an undead-turning cleric with spells, a gigantic thug with twice human damage-taking capacity, a monk whose fists equal weapons, or a wizard -- that wouldn't fit into 75-100 points and leave much for the traditional "couple of good attributes, couple of okay ones." And by upping the points and acknowledging that it's customary to start out with decent attributes, I immediately made skill levels quite high because of what GURPS assumes about skills.

My experience led me to conclude that, contrary to what many expect, attribute levels, feats, and spells -- even epic ones -- are the easiest thing to adapt. Skills are the real challenge, because they're kind of second-class abilities in D&D while they're the core of a GURPS character. In the end, this makes conversion difficult or impossible. I think it's better to come up with an abstract concept and build an entirely new PC that fits than it is to try to convert specific traits.

Re: Converting D&D DC to GURPS Skill penalties
 

It also fits with my assumption that you can half a D&D bonus/penalty to get a GURPS one (based on D&D's rule of thumb that a basic advantage or penalty is +-2, and GURPS' assumption that the same is a +-1). Thus, I'd say DC15 = +0, halve the difference from DC15, and round in whatever direction suits your mood.

Re: Converting D&D DC to GURPS Skill penalties
 

Only for adventuring use. A 1st level smith with an assistant or masterwork tools can reliably turn out masterwork tools and weapons if they have Int 12+. A 2nd level one, or a 1st level one with tools and assistant doesn't even need the above average Int. The same applies to most other non-adventuring tasks, and in this D&D isn't very different from GURPS, where a 'professional' level of skill (about skill-12) does fine for normal activities, but feels pretty marginal when out adventuring.

Re: Converting D&D DC to GURPS Skill penalties
 

I disagree... there are level requirements for skill, therefore you have to package your skill expertise with other, mostly combat related abilities, that a smith would not gain by default over his carrer.
Why is the old blacksmith that can make incredible items any better at combat, at resisting poisons, or pretty much everything else that's not related to blacksmithing?
Besides, I was refering to the high DC rolls that can only be done by higher-level characters, when GURPS specialists can be very high-skiled, pretty much independently of point-value, as long as you have enough for that one skill.
In D&D if you can't reach that target number, it's impossible, in GURPS you can allways try...

Re: Converting D&D DC to GURPS Skill penalties
 

I was responding to statements that low level characters have poor skill levels. This is not so, for non-adventuring tasks, and even for some adventuring checks.

He's probably not, seeing as even DC25 items, about as high as a normal check ever gets, can be managed by an Int 12 guy (+1) with Skill Focus (+3), MW tools (+2), an assistant (+2) and 7 ranks = +15 automatically using 'take 10', and that's all of 4th level.

And if they're low point characters specialists like that will die like flies in any sort of dungeon worthy of the name.

Not true. Once your adjusted skill drops below three in GURPS you can't succeed either. Also, in D&D you can get good enough to always succeed (there are no auto-failure rules for skills), whereas you can't do that in GURPS.

The games have different core assumptions, but if you're not looking at the very high end (points, levels), much of the stuff converts nicely with a bit of thought.

Re: Converting D&D DC to GURPS Skill penalties
 

The biggest one, IMO, is that DC is an "objective" measure of the difficulty of a task with no reference whatsoever to who is performing it. In GURPS, skill penalty is also a measure of the difficulty of a task, but it is meaningless unless it is attached to a specific character's skill - it is more "subjective." (Someone with Skill-20 is going to face a -6 penalty with a shrug; someone with Skill-10 is going to face the same penalty with soiled pants.)

The difference, if I may offer a horrible example, is something along the lines of: DC tells you how steep the hill is (and nothing else), whereas a GURPS skill penalty helps you determine how likely it is that *you* can make it to the top.

The absence of auto-failure and auto-success rules in d20 (the lack of a "1 & 20" rule) supports how DC works, while the presence of GURPS critical result rules supports how skill penalties work.

Re: Converting D&D DC to GURPS Skill penalties
 

And yet, if he wants to get better at smithing than that, bam, you run into arbitrary benefits. So master smiths that can handle DC 30 to DC 35 run into this. You can only stack so many bonuses until you can't stack any more.

Hilarious how people just can't seem to understand this very simple concept...

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.