A Simple Primer On Converting Between Systems

image It sits there in your hand, this awesome module that has an incredible story, a great concept, a well thought out adventure path, and it’s perfect for the game you’ve always wanted to run…. except it’s not in the system you or your group likes to play. While standing in the game store, you mull over your options. You could pick up the source books for the system and work to learn it, you could see if someone else who is more familiar with the system would run it for you, or you could try to convert everything over into the system you already know and are familiar with. Yeah, that’s the ticket… It won’t be that  hard, right….?

Converting a module or splatbook for use with another system is something that can increase your play options incredibly. There are a plethora of adventures and options books out there that might fit your group, but for one reason or another you don’t want to use the system they are presented in. So conversion is your best option, but how do you do it?

Figure out what you want from the source material and don’t do more work than you have to

The first thing to do when converting material from one system to another is to determine exactly what you want from the source material, then promise yourself not to do more work than is necessary to get that. Do you just want the adventure plot from a module? Do you want the one class from that Pathfinder splatbook, but in 4e? Are you going to use all the stats if your target system doesn’t have analogs for that?

The keystone rule of converting between systems, for me at least, is determining exactly what you need and not worrying about the stuff that doesn’t relate to that. My latest conversion was from 4e to Fudge. I dumped almost everything and didn’t worry about the stat block’s details. I looked over each and every one, but I only marked down what was necessary. The 4e power didn’t need to be converted exactly, but the feel of it did. If the enemy teleported 5 feet as a free action in 4e, it didn’t matter if I could find an exact duplicate in the target system. I wanted the idea of an enemy who could teleport at will, so I found the closest teleporting type power. If it isn’t close enough, fudge the details to get the feel in the target system. That is what is really important.

Don’t forget to see if a conversion has already been done

You are going to want to check one thing above all others before you start converting: Have other people already done the work for you? There are many conversion guides between systems floating around on the internet, and someone may have decided to make all the tools necessary to convert from one system to another. Do a quick search before you start in on the process of converting something between systems. You might not find a conversion for the exact module or splat book you are looking at, but you might find a guide that helps you do most of the dirty work.

What direction are you converting in? Use the right tactics

There are a few instances where your conversions between systems are going to be very easy, such as from a system like Pathfinder to D20 (or reverse). It might be from a system like 4e to Shadowrun, in which case you have similar levels of complexity, but different rules themes and goals. There are different tactics to use when converting between systems of different calibers, but you have to gauge the direction of conversion first. This is primarily the mechanically crunchy elements, but it doesn’t always have to be.

Heavy to Heavy

  • Heavily complex systems can convert well to other heavily complex systems.
  • Find overlap for the various elements. Focus on the things that affect dice rolling. Heavy systems tend to have light dice mechanics that are modified by many crunchy elements.
  • Make lists of corresponding powers. Is Mighty Cleave in one system most like Bashing Blow in another? Mark that down. Does Bashing Blow also fill in for the Doorbreaker power as well? Mark it down.
  • What is important in each system? If you are going between mechanically heavy systems, items might be huge sources of power in one system, while skills are the gamechanger in another one.

Heavy to Light

  • The key when converting from heavily mechanical systems to lighter ones is to find the core concepts of an element. Generally, you will be discarding a lot of the mechanical complexity, so you need to figure out what purpose an element holds.
  • Don’t question yourself if big things end up taking up less space in the new system. A mechanically complex system requires a lot of space to write down how a thing works. If the magic sword has a half a page in the heavy system, in the light system it might really be as simple as Magic Sword +3, Glows when evil is nearby.
  • Judge the power ratios. It is harder to determine exactly what a +4 gun in a heavily complex system equates to in a much lighter system, so look at it in the context of it’s original system. Is that weak, moderate, good, great, or Frigging awesome in the original system? Find the equivalent power level in the new system, don’t aim for a numerical conversion.
  • Heavy to light allows a lot of room for fudging elements to fit.

Light to Heavy 

  • Converting from a light to a heavy system is going to be a bit harder than other conversions. You are going to have to put in more work to build analogues. Similar principles apply.
  • Make lists of options for the heavily complex target system. When you are converting from heavy to light, you are going to have to fill in a lot of gaps. The +3 magic sword that glows when evil is nearby will likely need to have justifications in the heavy system. Is it the level 3 spell or the tier 2 power that enables that ability? How much does it add into the creation cost? Does this raise the character’s power level. The important thing is to make the element represent the same thing it did in the original system.
  • Don’t be afraid to change things to get the feeling of the thing being converted. In the light system, the vehicle that the group might be able to steal from some enemies has a purpose. What is that purpose? Is it to get them past a checkpoint, is it to help them in combat? Focus on that purpose and don’t worry about the rest. If the vehicle needs combat stats, then write those up because they are important. Don’t do it because they might be important. My caveat to that is this: You know how your group operates, and if they turn everything into combat options, then combat stats are important.
  • Beware of power level. Light to heavy conversions tend to suffer from power level imbalance. Heavily complex systems require a decent amount of power balancing, light ones don’t. Don’t stress yourself if the power balance gets a bit off, but ask yourself if a particular conversion will be too powerful or too weak at the party’s power level.

Light to Light

  • Converting from a light system to another light system is likely the easiest way to go. While there are going to be mechanical differences, they are not as heavily emphasized in light systems.
  • The core concepts are pretty much all you need to focus on. Generally, rules light systems use less mechanical methods of resolution. It might be as easy as saying “His strength is Pretty Good, so that means he is at Decent in the new system.”, but you will still have to look at what each element represents when you convert it.
  • Look at the themes of the target system. Rules light systems often focus on particular themes rather than broad implementations. The rules of the system often back up the particular themes and make it hard to run other types of games. That isn’t bad, but determine if  you need to bend the system a bit to meet the material being converted, or bend the material to meet the system’s themes.

Look for the overlap, make lists, fudge if you have to

After you’ve determined what your goal is from the source material, and know what direction you are converting in, now you want to look for the overlap.

  • What attributes are similar?
  • What skills correlate?
  • What powers are the same?

The more the source and target system have in common, the easier this is. However, if the source system differentiates between strength and dexterity, but the target system only has a body roll, then you’ve got a little more work. How do you determine how to split that up?

Well, in this case you want to make sure you are looking mostly at the destination system. The source system is important, but the destination system is what you’ll be running, so focus on that. Make a list of elements in the destination system, and use that to estimate things that don’t fit. Let’s imagine that our destination system has less attributes, but specializations to the attributes. Here is how we would tackle that.

  • Make (or find) a list of every mechanical crunchy element that centers around a certain area of the game, such as attributes. (I.e. All of the attributes, all of the feats that center around attributes, all of the powers that grant bonuses to attributes.)
  • Take the element and compare it to the list, looking for the easiest fit. If you can represent the agile rogue with a high agility type attribute that seems to match his level of skill in the source system, great.
  • If there are elements that don’t fit 1:1, then look for extra things in the target system to represent those abilities.
  • Look back over the thing being converted and determine if it gets the core concept well enough. Don’t be afraid to add in slightly rules illegal things to get the feeling of the element, even if they don’t fit 100%. *

Let’s take a look at an example of this.

  • First off, I  make a list of the attribute ranges in the target system  and what each area means. If the attributes in the source system are 1 to 18, but the target system is 1 to 5, I make a comparison chart somewhere that a 1 – 4 equals about a 1 in the new system, etc.
  • If the system has some vast differences in how to represent attributes (such as less attributes, but powers that enable more ways to use those attributes) I make a list of those as well.
  • With the lists in hand, I take a look at the stat block for the NPC and figure out that we don’t have an agility score, just a body and a couple of specializations. I decide that his body is only going to be a 3, but I’ll give him the Bouncy and Quick specializations which get the feel. He isn’t supposed to be completely badass, so I feel the 3 won’t make him a huge powerhouse on the strength side, but it will be enough to make sure he is good at agility rolls. If the system has a flaw system to hamper his strength a bit, I might make his agility a 4 and use a flaw to give him –1 or –2 on brawn rolls, depending on how the NPC is.
  • Wash, rinse repeat with skills, powers, etc.

* The Fudging debate is a hotly contested thing in gaming, but I don’t consider these types of actions real fudging. You are converting from one system to another and not everything will fit. As in step 1, the concept of what you are converting over is important. If that is a big, burly, nearly unstoppable tank, then you have to make some concessions to get it right in the target system. If what you end up with isn’t exactly like the source material but is still a big, burly, nearly unstoppable tank, even if it fudges a few level requirements, then you are golden.

You will not account for everything, so plan for fixing it on the fly

Whenever you convert from one system to another, you are going to miss a few things. Creating generic templates or quick reference options will often save you from game pauses. You might know what an element in the source system looks like, and you might have done a conversion of it to the new system, but when the PC whips out an odd power that you forgot they had and you have to roll a score that you didn’t account for in the conversion….well shit, what now? You can generally figure it out on the fly, but if you’ve got a generic template in the new system sitting around you are in a lot better shape.

Every system will be different though, so you have to determine what generic templates you need. In my current game, converted from 4e to rules light Fudge, I wrote up a bunch of generic materials:

  • Mundane weapons, Magic Weapons
  • Fighter NPCs (agile, magic, brawny, shooty)
  • Rumors that the PCs might find for plot hooks, linked to NPCs
  • Lists of names for NPCs
  • Lists of gossip going about town
  • Lists of locations

I went from Rules Heavy to Rules Light, so I can fudge most things pretty easily. I’ve made minimal use of my generics, but they’ve saved my butt when I’ve had to come up with things on the fly. Plus, they made me look like I’d accounted for everything all along and never had a gap in my planning.

How much of the source material can you continue to use?

As a final note when converting from system to system, determine how much of the source material you can use. Can you keep the book open in front of you and just use post-it notes to mark differences? Are you going to have to re-write almost everything? If you have the PDF, can you copy and modify what is needed? The more of the source material that you can use, the easier you’ll find the conversion.

If you find yourself needing to make a lot of changes though, that doesn’t mean it is all bad. When putting together lists and other tools to help yourself convert, you’ll likely be building a toolkit to convert ANYTHING from the 2 systems you are looking at. The next time you convert from the source system, you’ll probably be able to do it quickly.


These are the steps I use when converting material between systems. There are always going to be things that are unique to the conversion process between any 2 systems, but a lot of the core concepts are pretty similar. I hope this helps people looking to convert, but I want to hear what things you do when converting between systems. What are your key tactics for converting between systems? Got any horror stories when you missed something? Drop a line in the comments and tell me what you think.

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John Arcadian is a writer, gamer, art director, web designer, crafter, and kilt-wearer. You can find more of his writings on gaming over at http://gnomestew.com. For web-design projects, check out http://beezenwebdesign.com.
  1. mcmanlypants     | Reply

    I am always terrified of converting something from one system to another so I love the way this post breaks it down. That said, I cannot condone fudging level requirements or the like to retain the flavor if that would mean generating an NPC with abilities that are not also available to PCs of equivalent level/power/etc. That sense of a GM having “cheated” to make an NPC “better” than the PCs seems to be the one thing that I have found myself resenting most as a player and the thing my players have seemed to resent most when I was GM.

  2. Razjah     | Reply

    What if the NPCs are better? I don’t think fudging a little to skimp requirements for abilities that make the character is that bad. Many games have a group of PCs fighting a superior foe, I don’t really see fudging to make that foe actually superior as a bad thing. I would rather the fight be spectacular because I fudged a little for requirements to an ability the NPC had.

    If I play a good character I don’t really see anything wrong with the evil NPC making a bargain with a demon for additional power- I guess I look at fudging in a similar way.

  3. Roxysteve     | Reply

    But how do you reconcile your implication that buying the books and learning the system is a rejected approach (because if it isn’t, then the subject of the article goes away) with the comment “If it isn’t close enough, fudge the details to get the feel in the target system“?

    To make that assessment you must be familiar enough with the original system to be able to interpret what you are seeing.

    For example, reading an NPC stat block in, say, GURPS or FATE if you have never come across the materials for them is a speculative affair that permits no real interpretation of how the character is supposed to look and behave.

    Yes I know FATE doesn’t have stats (and some people feel the term stats is misapplied) but my point stands.

    Put another way: Without any knowledge of Savage Worlds, how do I properly assess my guestimate value of D6 strength for the original D20 value of 13?

    I hold that without at least some knowledge of what the original system is attempting to achieve one cannot make a faithful conversion of any sort. D20 mechanics are not intended to emphasize the same things that BRP mechanics emphasize, and the BRP rules aren’t trying to do what GURPS does. Without an understanding of the key emphasis of an RPG system I doubt such a conversion can be faithful.

    A very interesting article and a stimulating subject in general. I look forward to future articles on this theme.

  4. 77IM     | Reply

    Great article!

    Over on the PEG Savage Worlds forums, the refrain is “convert the flavor, not the mechanics.” Basically, you imagine the game world/setting completely without rules (like, if it were being made into a book or movie) and then create rules from THAT, instead of looking directly at the original rules. This helps people avoid the pitfal of trying to convert game mechanics unnecessarily.

    This is very similar to your advice to focus on core concepts and ignore stuff that doesn’t matter.

  5. John Arcadian - Post Author     | Reply

    @mcmanlypants – You’ve definitely got a point on fudging being bad if it makes the NPC too powerful. My take on it is this. If whatever power (let’s say an ability that lets them break through stone walls) that was absolutely necessary for the NPC to have required level 12 or 18 strength in the target system, I would just give the NPC the power without the other adjustments. They could still be a level 5 enemy and appropriate to the party’s general level, but they would have a much higher power. If the game system I’m converting to is heavily mechanical and requires balance, I’d see if I could adjust something else or I’d use the enemy effectively, but not dickishly. If the concept I need that enemy to have is that they can bust through stone walls, I’d remove or ignore the part about them being able to break bones without a roll or critically incapacitate any PC struck by their charge. Leaving that stuff in and turning the low level encounter into a bloodbath wouldn’t be fun. Letting the NPC be able to break through walls in order to facilitate some part of their background would be, in my mind, an acceptable fudge of the system.

    @Roxysteve – Whenever you decide to convert from a system, you are going to have to be a bit familiar with it. You can pull a decent amount of context clues from a statblock, but the real meat of what you want to convert is in the descriptions, usually. Looking at the statblock with no knowledge of the source system can still tell you some things just from the context clues. It can tell you that the NPC has the ability to teleport up to 25 feet, has a high agility (compared to their other stats), and has a sword that deals high damage. That’s useful information, but a bit of knowledge about the source system can expand upon it and help you get a better mechanical representation in the new system. The description is what really gets transferred though. It is whether or not the teleporty, agile sworduser is Nightcrawler, a demon with a flaming brand, a human with access to a nifty spell, etc. The salient details are more often found there, and the mechanics need a correlation in the new system.

    @77IM – Thanks. I like that idea for the approach.

  6. Scott Martin     | Reply

    I’m probably too mulish–or, more, I just don’t appreciate written adventures enough to go to this level of fidelity in converting. I can see real advantages to going the full depth, as you laid out brilliantly… it’s just not something that appeals to me enough to do right. Inspiration is most of what I’ll grab from another system.

  7. Pingback: Ravenous Role Playing » Blog Archive » Friday Five: 2012-03-30

  8. Silveressa     | Reply

    Another thing to keep in mind with conversions once you’re done, is “Can you share this conversion publicly?” Depending on the game system, some companies have a hard line “no conversions ever” policy. (Like Palladium Books does)

    Even if a company does have such a policy, it can be worth asking around on gaming site (like rpg.net) and seeing if someone has still converted the game to/from a particular rule system and is willing to share the conversion with you privately.

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John Arcadian