Converting DND 3.5 DC to DFRPG
 

There is a particular DND 3.5 adventure (Necropolis) I want to run using DFRPG. I would like to avoid having to convert everything ahead of time. I will be winging it on the monsters or using the closest DFRPG analog I can find. However, for traps, locked doors, etc., I wanted to see if there was a way I could convert the DND 3.5 Difficulty Classes ("DC") for these tasks to a (range of) DFRPG difficulty modifiers for the analogous exploit.

The problem is the DC scale is linear, while the DFRPG has a bell curve. Has anyone done such an analysis and arrived at a conversion of DND 3.5 DC to DFRPG difficulty modifiers? Thanks.

Re: Converting DND 3.5 DC to DFRPG
 

The easiest way is probably just compare the Task Difficultly Modifiers to the generic DC table and match similar descriptors. So:
DC 0=Very Easy=+6 or +7
DC 5=Easy=+4 or +5
DC 10=Average=+0
DC 15=Tough=Unfavorable=-1
DC 20= Challenging= Hard=-4 or - 5
DC 25 =Formidable= Very Hard =-6 or - 7
DC 30= Heroic= Dangerous = -8 or -9
DC 40 = Nearly Impossible = Impossible = -10

The difficulty with a more rigorous approach might be to say that to have a 50 % of DC 10 you need skill 0 which would therefore be statistically equivalent to Skill-10, but that means that untrained skills in D&D are better than GURPS defaults by about 40-48%. If instead you assume that default use is equivalent, "Average" difficulty in D&D is actually equivalent to Very Easy to Easy in GURPS, which makes it non-trivial to assess what the equivalent of Skill-10 is. At any rate once you have decided on what Skill-10 is equivalent to you can use that baseline and the fact that each +1 to DC is - 5% chance of success and compare that the Probability of Success table and then subtract 10 to get a modifier.

Assuming +0=Skill-10 then:
DC 5=75%=~Skill-12=+2
DC 10=50%=Skill-10=+10
DC 15=25%=~Skill-8 = -2
DC 20=5%=~Skill-5 = -5
And then you run into the problem that nothing higher is even possible to roll on 1d20 whereas 3d6 goes down to half a percent.

Re: Converting DND 3.5 DC to DFRPG
 

Thanks, sir pudding. I like the simplicity of your first suggestion and will give it a try.

Re: Converting DND 3.5 DC to DFRPG
 

Maybe this is overly simplistic, but I treat a DC 15 task as skill +0, and add +2/-2 to skill for each 5 points above or below that. Easy enough to remember:

DC 5: +4
DC 10: +2
DC 15: 0
DC 20: -2
DC 25: -4
DC 30: -6
DC 35: -8
DC 40: -10

Then I'll add or subtract another +1 for the numbers which are more than 1 DC off from a multiple of 5. So DC 19 and 21 are -2 just like DC 20, but DC 17 and 18 are just -1, and DC 22 and 23 are -3.

Note: I haven't played much D&D 3.5, so I can't say if these are exactly right, but the module I converted seems to have a lot of DCs in the 15 to 25 range, and this yields modifiers in the 0 to -4 range, which seems like a reasonable challenge for Dungeon Fantasy characters, who tend to have pretty good ability and skill levels. And it has occasional DCs in the 40 range for tasks that are supposed to be very hard, and a -10 does reflect very hard (but not impossible with high skill) pretty well. So I've been pretty happy with this simple system.

Re: Converting DND 3.5 DC to DFRPG
 

Note that a 1st level D&D 3.5 character with a Stat of 10-11 and max ranks (4) in a skill for a total of +4 has a 50% chance of making a DC15 check, and DC15 is what d20 systems tend to think of as a average check. Thus +0 for DC15 is about right - someone with some training an no great talent will have about skill-10 in GURPS.

D&D 3.5 tends to consider an situation that would give a modifier worth a +-2, so where something would give that, give a +-1 in GURPS (masterwork non-combat gear does this,m for example, while 'good' equipment gives a +1 in GURPS).

Jumps in DC in D&D usually come in 5-point chunks unless part of some formula, while B343-344 uses 2-point increments for difficulty, so each +5DC would give a -2 penalty (as other posts also suggest). If this doesn't seem to make life hard enough, just go to -3 per step.

Re: Converting DND 3.5 DC to DFRPG
 

In 3.5, DC 10 was defined as "Average"; DC 15 was "Tough".

Re: Converting DND 3.5 DC to DFRPG
 

Thanks. I'll have to compare the module's DC settings to the character's skill levels and figure out which conversion chart yields the most playable results.

Re: Converting DND 3.5 DC to DFRPG
 

And in GURPS, a difficulty +/-0 task is a typical task for adventurers.
Speaking as someone who has done this conversion many times, I go with D&D DC 15 = GURPS task difficulty 0.

Re: Converting DND 3.5 DC to DFRPG
 

If you are converting adventures meant for low level characters for 250 point delvers having tasks be -1 instead of +0 is probably a feature.

Re: Converting DND 3.5 DC to DFRPG
 

The adventure I plan on converting (Necropolis) is for level 10 to 15 DND characters.

Re: Converting DND 3.5 DC to DFRPG
 

Shows how long since I've looked at the v3.5 rules. These days most things seem to start at DC15 in d20 games.

Re: Converting DND 3.5 DC to DFRPG
 

Well some tasks are definitely lower. Identifying a common CR 5 or less monster or many crafting checks for normal quality items for example. Otherwise yes, but presumably that is because Average tasks are supposed to be things that low level commoners and experts (i.e. most everybody) have a reasonable chance of success at; if they could do the things in adventures they wouldn't need to find adventurers to give quests to.

Re: Converting DND 3.5 DC to DFRPG
 

Low-level Commoners and Experts should generally be 'taking 10', given the nature of their lives, and getting a +5 bonus so your 'take 10' always passes DC15 isn't hard if it's your primary skill.

Even DC20 isn't that hard if you have an assistant. 4 ranks, +3 feat, +2 MW equipment = +9. Add an assistant's +2 'assist another' (and if they've got the same stuff as you, they succeed even on a '1'), and you can take 10 to auto-succeed on a DC20 task, such as working on a masterwork piece of gear. That's a 1st level character with unexceptional stats. A 3rd level character can do without either the assistant or the MW gear. A 5th level character needs neither. Better stats obviously allow these milestones to be reached sooner.

But yes, 'average' at DC10 was obviously set there using low level ordinary people as the baseline.

Re: Converting DND 3.5 DC to DFRPG
 

Another conversion question. The DND 3.5 adventure Necropolis has stats for many doors, walls and other terrain features using Hardness and HP. Hardness is the equivalent of DR in DFRPG while HP is the equivalent of HP. However, I am not sure how they scale between systems. Anyone have any ideas on a conversion formula?

BTW - I really appreciate how helpful everyone is. Thanks.

Re: Converting DND 3.5 DC to DFRPG
 

I would just ignore the D&D numbers and use the GURPS values for the same materials.

Re: Converting DND 3.5 DC to DFRPG
 

Hence why DC 15 is the norm for adventuring tasks. The DMG (p. 31) as DC 15 for clear GURPS difficulty ±0 tasks like stabilizing someone below 0 hit points and doing a fast-talk on a guard. It's pretty easy to get that DC for abilities, For example, a first level wizard can get the Save DC for his spells up to 15 without much trouble: 10 + spell level 1 (best he can lob) + Int 16 (+3) + Spell Focus (whatever school) = DC 15.

Or, let me put it another way: using DC 10 as task difficulty ±0 will lead to a lot more bonuses on rolls than we're used to seeing in GURPS.

On this matter, however, I agree utterly. When converting, you should make things as native to the new system as possible. The point is to run the new system, not to mimic D&D perfectly. If you're going to do that, you might as well run D&D.

Re: Converting DND 3.5 DC to DFRPG
 

Understood and agreed.

Re: Converting DND 3.5 DC to DFRPG
 

No, the converse would be the case. Your method says DC 15 = +0 whereas my proposal has it at -1.

You are right about many specific tasks though. Though not all. Identifying a dire panther is probably not more than +0, for example, but that is probably coincidence resulting from the CR system more than anything.

Re: Converting DND 3.5 DC to DFRPG
 

You're right about the sign, though the amount is -2 (there’s no way lowering the chance of success 25% is a mere -1 in GURPS, as the biggest jump on the 3d6 chart is half that for adding 1). But you’re flat out wrong about most rolls being at -1 (or -2) being a feature; it’s a bug. It’s annoying to figure and remember (D&D phased out many little such modifiers for this reason starting in 4e), it hoses the players who bought their skills at 15 or 18 or whatever and expect to be rolling at those levels most of the time.

Furthermore, they’re 250 points. A 1st level D&D character is expected to be able to make a DC 15 roll half the time in something they’re good at, and he’s weaker than a 250-point DF character. Not only is a DC save common for a first level character, but a DC 15 AC (if you want to think of it that way) is common at that level as well, even without a Dex bonus (GURPS Dodge). A 250 point DF character is something like a 6th level D&D character; he’s supposed to be making rolls with ease. They’re supposed to be cruising through adventures for low-level characters.

Re: Converting DND 3.5 DC to DFRPG
 

My proposal was just to use GURPS modifiers and base them when needed on the equivalent category label, it deliberately eschewed a rigorous mathematical approach because that kind of approach assumes DCs make much sense in the first place.

There are few examples of traps in DFRPG that are +0 to detect and disarm, so that would appear to be a bug that isn't already in the game.