Converting D&D to GURPS: Combat Comparison

[abates17]

I wanted to try my hand at a quick monster conversion from D&D to GURPS, and I checked my results with a combat example. Let’s see how it goes!

Skeleton (D&D 3.5)
Str 13, Dex 13, Con 0, Int 0, Wis 10, Cha 1
Hit Dice: 1d12 (6hp)
Armor Class: 15 (+1 Dex, +2 natural, +2 shield), touch 11, flat-footed 14
Speed: 30 ft.
Attack: Claw +1 melee (1d4+1)

Okay, let’s start the conversion! Based on suggestions from others on the forums, I am converting Str directly to ST, and halving any differences between the other attributes and 10. (So for example, Dex 14 = DX 12, Dex 8 = DX 9, and so on.) The idea here is that attributes in D&D give a bonus (or penalty) based on 1/2 the amount off from 10, and GURPS gives a straight bonus (or penalty). With that in mind, we get:

Str 13 => ST 13
Dex 13 => DX 11
Wis 10 => Will 10 => Per 10

Normally, I would convert Int to IQ and Con to HT, but both values are 0 in D&D, which makes no sense to me. Since Wis is already 10, I’ll just set IQ to 10 based on that, since I doubt it will come up anyway. As for HT, let’s see if we can reverse-engineer a value based on Basic Move (which is based off DX and HT).

The skeleton has Speed of 30 ft., so we should be able to figure out Basic Move based on that. A round in D&D is equivalent to six seconds, while a GURPS round is one second. However, a creature can take two Move actions in a D&D round, so Speed should be divided by 3 to get the equivalent GURPS Basic Move (and converted from feet to yards, of course). So that leaves us with

Speed: 30 ft. x 2 moves per round = 60 ft. / 6 seconds per round = 10 ft. = 3.33 yards => Basic Move 3.33 (dropped to 3)

Now we know that in GURPS, Basic Speed is (HT+DX)/4, which means that (HT+DX) = 13.33, which gives us an HT score of 2.

HT 2
Basic Speed 3.33
Basic Move 3
Dodge 6 (Basic Speed + 3, dropping fractions)

Okay, doing well so far! Just a few more things to do, then we can check our numbers. Let’s get some combat data in here. Based on the given AC bonus of +2 natural, divide that by two to get:

Natural DR 1

It says he has a shield, so we can figure:

Shield = DX - 4 = 7

As for Block, Dodge, and Parry values, the Parry score is 3 plus 1/2 Attack value. Let’s assume a base attack value of 10 (more on that in a minute) plus the +1 bonus makes it 11, which leads to:

Block = 3 + 1/2 Shield = 6 (8 on shield side)
Dodge = 6 (8 on shield side)
Parry = 3 + 1/2 Attack = 8 (10 on shield side)

Now, time to check our numbers with a combat example! Let’s pit skeleton vs. skeleton to figure out hit percentage and average damage. First, the D&D combat data:

D&D: Attack D20+1 vs. AC 15 means the attacker hits 35% of the time. At 1d4+1 damage on a hit, that means that the average damage is:

(3.5 * 35%) = 1.225 average damage.

Now, let’s see if we can get similar numbers from GURPS combat…

I’m assuming a basic attack skill of 10, plus the +1 Claws attack bonus puts skill at 11. With skill 11, the attacker will hit 63% of the time. Now, the defender’s Parry is 10 on the shield side (50%), and 8 on the other side (26%). I’ll figure attacks from the front will be on the shield side 2/3 of the time (I know, this is very quick and dirty), so the weighted Parry percentage is 42%. Using the same calculations, we get Block 20% and Dodge 20%. Average those all together (figure an equal chance of any defense), and we get the defender succeeding 27.3% of the time.

SO…the attacker hits 63% of the time, and the defender succeeds 27.3% of the time. This leads to:

(63% * 72.7) = Attacker damages defender 45.8% of the time.

Okay, 45.8% is higher than the D&D hit percentage of 35%, but we haven’t figured damage yet. Average damage for 1d4+1 is 3.5, minus the skeleton’s DR1 equals 2.5. This means that the average damage is:

(2.5 * 45.8%) = 1.145 average damage

Not bad! With our converted numbers (and some hand-waving), we get 1.145 average damage in GURPS, which is reasonably close to the 1.225 average damage in D&D. I think that is a good sign that our conversion (at least for the sake of combat) is pretty accurate.

Thoughts? Comments? Suggestions?

[chris1982]

Originally Posted by abates17

I wanted to try my hand at a quick monster conversion from D&D to GURPS, and I checked my results with a combat example. Let’s see how it goes!

Skeleton (D&D 3.5)
Str 13, Dex 13, Con 0, Int 0, Wis 10, Cha 1
Hit Dice: 1d12 (6hp)
Armor Class: 15 (+1 Dex, +2 natural, +2 shield), touch 11, flat-footed 14
Speed: 30 ft.
Attack: Claw +1 melee (1d4+1)


Thoughts? Comments? Suggestions?

My honest opinion is that you are totally overengineering the whole thing and your results are quite a bit off at some points.

Here is my take (using just common sense):

ST 11 (If based off a strong human)
DX 10 (typical human as base)
IQ -
HT -

HP: 10 - destroyed at 0 HP
Will 10, Per 10
Move 5, dodge 8 (10 w. small shield)
DR 1
No brain, no vitals, impaling and cut damage do only 1x damage

Attack: Brawling 12 (claw) 1d cr
Defense: Block (Shield) 11

Et voila.

[Captain-Captain]

Formulistic conversions from RPG X to RPG Y almost always fall apart. Basic assumptions don't synchronize and after a while, it shows.

30 feet is standard for D&D character movement. In D&D Con and Dex scores bear NO influence on move. High STR does not unpenalize armor movement penalties though actually using ligher material (mithiral) does.

So Zombies in D&D have the same movement as a normal human.

THAT is the base you use for conversion.

[Harald387]

The 'Skeleton' template in GURPS Magic is pretty much the standard D&D 3.5 skeleton and makes a great fodder monster.

[zorg]

Originally Posted by chris1982

My honest opinion is that you are totally overengineering the whole thing and your results are quite a bit off at some points.

Originally Posted by Captain-Captain

Formulistic conversions from RPG X to RPG Y almost always fall apart.

I agree.

Instead of translating the mechanics point for point, it is usually easier and more efficient to just look at the *description*, and stat that in Gurps. This also gives better results, most of the time. Imo, converting mechanics has no advantage at all.

Your HT 2 is a good example of that. You got HT2 by using a pretty convoluted process, and the result greatly impacts the Gurps output: your skelly has an abysmal Move, Dodge and is exceedingly easy to destroy. A simple punch can kill the poor thing! This is neither supported by "traditional" Fantasy skeletons, nor is it true - afaict - for the D&D Skeleton.

It is easier to set the overall toughness (as represented by HT) to a more or less human standard (10ish), and add traits to reflect the undead nature of the skeleton.


That said, if you enjoy this sort of tinkering and are OK with the result, then go for it.

[roguebfl]

Originally Posted by zorg

It is easier to set the overall toughness (as represented by HT) to a more or less human standard (10ish), and add traits to reflect the undead nature of the skeleton.

Like Fragile (Brittle) and Fragile (Unnatural)

[zorg]

Originally Posted by roguebfl

Like Fragile (Brittle) and Fragile (Unnatural)

Right - if you even want to bother checking the correct traits. For a monster, it's sufficient to note "Destroyed upon reaching 0 HP, double damage from crushing attacks."

[abates17]

Originally Posted by chris1982

My honest opinion is that you are totally overengineering the whole thing and your results are quite a bit off at some points.

Here is my take (using just common sense):

How are my results “quite a bit off”? At least in terms of combat, I thought they were a pretty good match.

Originally Posted by Captain-Captain

Formulistic conversions from RPG X to RPG Y almost always fall apart. Basic assumptions don't synchronize and after a while, it shows.

I’m trying to use such conversions as a starting point, not as a finished product. I want to avoid the “common sense”*or “eyeballing”*conversions that happen, because I can make those adjustments to the finished result if necessary. I was just trying to see if I could come up with a reasonable method of converting a D&D stat block to GURPS. Except for calculating Basic Move, I thought I got pretty close.

Originally Posted by zorg

You got HT2 by using a pretty convoluted process, and the result greatly impacts the Gurps output: your skelly has an abysmal Move, Dodge and is exceedingly easy to destroy. A simple punch can kill the poor thing!

My HT result did not have an effect on Move or Dodge; it was reverse-calculated based on those. And if a simple punch could kill the skeleton, how is that any different from the D&D version, with 6 hit points?

Really, I didn’t mean to come on here, ask for suggestions, and then act like I’m ignoring everyone’s criticism. I just think that there is nothing wrong (in principle) with coming up with a stat-conversion formula, at least as a starting point for further calculations. Thanks for the advice on Basic Move though; if I divide D&D Move by 2 instead of 3, I get a GURPS Basic Move of 5, which leads to a HT score of 9, which seems much more reasonable for a monster like this. Obviously I will have to add various traits like Fragile (Brittle or Unnatural) and damage modifiers, but I thought this was a pretty good start. I guess I’m in the minority though.

[Harald387]

Originally Posted by abates17

How are my results “quite a bit off”? At least in terms of combat, I thought they were a pretty good match.

The big, glaring issue is the HT score: Your skeleton automatically fails any HT roll he makes, unless he's getting a bonus on it. You can exempt him from several of them based on his unliving nature, of course, but HT rolls get used for resistance to various spells that probably *should* affect a skeleton (he'd never be able to resist them), as well as Major Wound checks (he'll ALWAYS be knocked down by any attack dealing half his HP or more). As others have noted, this also gives him an abysmal move and dodge score, which are definitely not in keeping with the D&D skeleton concept.

Originally Posted by abates17

I’m trying to use such conversions as a starting point, not as a finished product. I want to avoid the “common sense”*or “eyeballing”*conversions that happen, because I can make those adjustments to the finished result if necessary. I was just trying to see if I could come up with a reasonable method of converting a D&D stat block to GURPS. Except for calculating Basic Move, I thought I got pretty close.

My HT result did not have an effect on Move or Dodge; it was reverse-calculated based on those. And if a simple punch could kill the skeleton, how is that any different from the D&D version, with 6 hit points?

The problem with calculating Move based on the D&D move of 30' is that, in D&D, normal humans also move 30' - if you use the same standard for conversion, average HT for a human becomes 2 as well, which is obviously not the case.

A better way to look at it is 'in D&D, the average human has a move of 30'; in GURPS, the average human has a Move of 5; therefore, anything that moves 30' in D&D should move 5 in GURPS'.

It really is better, in general, to try and convert concepts rather than direct mechanics. It's also (in my experience having tried both) faster, once you get into the swing of it.

[Icelander]

Another problem with using Move to derive the HT is that you've compared apples to oranges. GURPS Move is the top speed of the character while D&D Move is a tactical movement that aims to avoid triggering the dreaded Attacks of Opportunity.

Characters in D&D that do nothing but Run for a turn can move at x4 speed, as far as I remember. That gives us a 120' or 40 yards over a 6 second period.

The same normal character in GURPS can move his full Move score in the first turn and Movex1.2 for the other five seconds. That means that a Move 5 character can cover 41 yard in 6 seconds.

It appears pretty clear to me that a creature with 30' Move in D&D has normal human movement, which in GURPS is Move 5.