OK RPG Rules: Basic Mechanics

The Rank Chart

This table is the core of the rules. Learn to appreciate it, because you will be using it, implicitly or explicitly, almost every time you use the rules.

Rank Abbv Base
Number Halved
Pathetic Pth -2 (1/5) 0.2 Def (1/2) 0.5
  Pth+ -1 (1/3) 0.3 Def (1/2) 0.5
Deficient Def 0 (1/2) 0.5 Def+ (2/3) 0.7
  Def+ 1 (2/3) 0.7 Def+ (2/3) 0.7
Average Avg 2 1 Avg 1
  Avg+ 3 1.5 Avg 1
Good Gd 4 2 Avg+ 1.5
  Gd+ 5 3 Avg+ 1.5
Great Grt 6 5 Gd 2
  Grt+ 7 7 Gd 2
Extraordinary Ext 8 10 Gd+ 3
  Ext+ 9 15 Gd+ 3
Heroic Her 10 20 Grt 5
  Her+ 11 30 Grt 5
Legendary Leg 12 50 Grt+ 7
  Leg+ 13 70 Grt+ 7
Mythic Mth 14 100 Ext 10
  Mth+ 15 150 Ext 10

(In principle, the table extends infinitely far in both directions; in practice, this is about as much of it as you'll need. Should they come up, ranks beyond Mythic are (Mth+1), (Mth+1)+, (Mth+2), etc. Similarly, ranks worth than Pathetic are (Pth-1)+, (Pth-1), (Pth-2)+, and so forth. Base successes, number, and halved ranks continue their pattern unaltered in both directions.)

An increase or decrease of one rank corresponds to two rows on the table; a difference of one row is called a half-rank. The abbreviations FR and HR will often be used.

The first two columns of the table are hopefully self-explanatory. The third column, Base Successes, is not strictly necessary, since the number of successes matches one-to-one with the number of half-ranks above Deficient, but many players find it easier to add and subtract numbers than count half-ranks up and down.

The fourth column, Number, is easy to use but complex to explain. It's used to correlate abstract ranks with concrete numbers or measures in the game world. Each increase of three full ranks corresponds to a factor of approximately 10, so one half-rank is a factor of 1.5,one rank is a factor of 2 and two ranks is a factor of 5. After 10, then pattern repeats 15, 20, 30, 50, 70, 100, 150... It also repeats in the downward direction, 0.7, 0.5, 0.3, ..., but the fractional equivalents are more likely to be useful. This mapping of addition to multiplication (and hence, subtraction to division) is referred to as logarithmic scaling.

The Halved Rank of a rank is what you would get if you halved the distance between that rank and Average (and then rounded downward). This rank is used when the spread of some Attribute or quantity needs to be reduced, either to keep values beyond Pth or Mth from cropping up all the time, or to better match the real world. The last column is just the number of the Halved Rank, which you could find by looking up the Halved Rank, but is duplicated here for convenience.

Calculations with the Rank Chart

This is really not as complicated as it sounds. Honest.

Multiplication and Division

Sometimes you will convert a rank directly to a number, but more often you will want to divide or multiply the number of one rank by that of another. Although you can do this in the usual way, you can also divide by finding how many ranks separate the two numbers and counting that many ranks from Average (ie, 1), or finding the rank of the number you want to multiply by, and adding that many ranks. For example, to find how many strong men (Good Strength) a Heroically-muscled beast-man is equal to, stare at the chart until you realize that Gd and Her are three full ranks apart. If you count up 3 ranks from Average, you get to Extraordinary, the number for which is 10: the beast-man is as strong as 10 strong men. To find out what rank an evil mutant twice as strong as the beast-man has, find the rank of the number 2 (a full rank away from Average) and add that to the rank of the beast-man's Strength: Legendary Strength.

Irregular Numbers

Since virtually all numbers you encounter in the rules will be on the table, using the table for calculations will ensure that you always get another number on the table. If you do the math by hand, or if you use arbitrary numbers, you will often get results not on the table, in which case you will normally use the next lowest number that is on the table to find the rank. EG, 12 drops to 10 (Extraordinary), 2.5 to 2 (Good), and so forth.


If you want to add the numbers of two ranks, instead of adding the ranks themselves (which would multiply the numbers) using the chart, there are only three possibilities:

If you have more than two numbers, first multiply together any sets that are equal. Then add the largest two, then add the next largest to that sum, and so forth until either you've added all the numbers, or you get to two numbers separated by more than a full rank (in which case none of the smaller numbers will affect the final sum).


Like addition, subtraction works on the difference between the ranks of the two numbers. Because the logarithmic scale, although it can express arbitrarily small numbers if you go far enough below Pathetic, never reaches zero or negative numbers, you can only subtract smaller numbers from larger ones.

Basic Action Resolution

The primary purpose of game mechanics in an RPG is to objectively determine what characters can do, cannot do, and might be able to do. In the OK RPG Rules, you do this by comparing the rank (or successes) of your ability to do something to the rank (or successes) expressing the difficulty of the task. If your ability is equal to or greater than the difficulty, you succeed; if not, you fail.

If your ability was just the rank of an Attribute, this would be an easy calculation, but very predictable and not much fun. To express the uncertainties of life that afflict even the most heroic, and to add excitement to the game, the rank of your Attribute is modified by the roll of dice when determining success or failure.

Each die needs to have an equal probability of producing the results -1, 0, and +1. FUDGE dice, labelled with two -s, two +s, and two blanks, work well for this, but you can also use regular 6-sided dice, reading 1-2 as -1 and 5-6 as +1 (or, for the determinedly nonconformist, 12-sided dice with 1-4 as -1 and 9-12 as +1). The sum of all the dice rolled indicates how many half-ranks to add to or subtract from your Attribute for this test. Regardless of how many such dice you roll, the average roll is always +0, and you have the same chance of rolling +N as -N (for any N up to the number of dice (okay, if N is more than the number of dice, the chances are still equal: they're both 0)).

The standard number of dice to roll is 4, producing a result of anywhere from two full ranks below to two full ranks above your base Attribute. Any time it's indicated or implied that you need to roll, but no number of dice is given, you roll 4 dice. In some circumstances where less variation would be more appropriate, you may be asked to roll only two dice, or even only one die. (The latter is typical for contests of strength, speed, or other forms of raw energy output; four dice would have the result range over a factor of 20, which is ridiculous.) When you need to roll fewer than four dice, the number will be given specifically.


You will usually know what the difficulty of an action is when the GM tells you. In principle, the difficulty could be kept secret, but since (as you will see below) you must know by how much your roll exceeded the difficulty, and you are capable of basic subtraction, you will know what the difficulty is after the first roll.

Any sort of action that is opposed or resisted by another character (which is true of the majority of actions you are likely to attempt) will have a difficulty equal to her Attribute, possibly modified by circumstances favoring one side or the other (eg, it's harder to slug someone who's spending some of her precious few Action Points to dodge your blows, but if you do manage to knock her out, it'll probably be easier to persuade her buddy to run away).

This can apply even if the other character isn't directly involved or isn't even present: if you're trying to break into a computer system with security set up by a hacker of Extraordinary skill, the difficulty will probably be Extraordinary (maybe worse if he obsessively devoted all his time to plugging security holes), even if he's long gone.

When your action is opposed only by the laws of physics and the perversity of the inanimate world, the GM will, frankly, just make something up. The rule of thumb is that a task of given difficulty is about even odds for someone of the same rank (60/40 in favor of success), and almost certain (94%) for someone a full rank higher, so the GM will set the difficulty according to what kind of rank would be challenged by the task, or would be easily able to accomplish it.

Extra Successes

If your roll is exactly equal to the difficulty, you get a marginal success: as poor as you can do without actually failing. To do better than that, you need to exceed the difficulty with your roll. Every success (equally, every half-rank) you get beyond the difficulty can be spent to improve the result of your action in some way. You don't need to decide how to spend your extra successes until you actually have them and know how many there are.

When spending your successes on something concrete enough to have a rank or number, there are three possible rates of return: one half-rank per success, one full rank per success, or one full rank for each success up to a certain number and one half-rank for each success beyond that. It is considered good form for the GM to decide which of these applies before you roll, to avoid the temptation to adjust your results to fit a preconceived notion, but sometimes a preconceived notion about level of success is necessary to the plot.

If no specific decision is made, assume one half-rank per success as the default.

Because the possible range of actions is infinite, the ways in which actions can be improved are also infinite, but tend to fall into four categories.


If the length of time it takes you to accomplish something is important, the GM needs to specify some base time for the task, which you can then reduce by spending successes. Reducing time is almost always done at a half-rank per success.

Optionally, if you fail the roll by only a success or two, the GM may let you succeed marginally after a time increased by a half-rank for each success you lack. However, the base time will usually be set to be exactly equal to the time you have until the next crisis, so this rule will seldom apply.


This is the most promiscuous of the four categories, since "quality" can mean so many different things. In the OK RPG Rules, however, it will usually be the case that one success applied to quality will improve the result in by one half-rank in some measurable way. For example, when jury-rigging repairs to a vehicle, extra successes could increase the time or distance until it breaks down again. When trying to lose a tail, extra successes could increase the difficulty of following you. When building a weapon, extra successes could increase the damage it does (although this would probably require several successes per half-rank).


Some tasks have the potential to produce or affect a variable number of objects or people (building flintlocks to equip your new, formerly Neolithic, allies; raising an army of the undead). On a marginal success, the number is usually 1 (maybe 1 per day in the flintlock example). Usually this can be increased by one half-rank per success (2 success for 2, 6 successes for 10, etc), but if the number can be both variable, and large, it might go up one rank per success (6 successes now gets you 100). If there is some number larger than one that the GM feels should be characteristic of such actions, then one success gets a full rank until that number is reached; additional successes get only a half-rank each.


Spending a success on style has no direct mechanical effect, but makes you or your results look better, which might impress your fellow players and will probably impress any NPC witnesses. The exact effects are so strongly dependent on what you're doing, how you're doing it, and your character's personality and personal style, that no guidelines can really be given. Generally, anything that isn't inappropriate for the tone of the game and can't be leveraged into a dozen times infinite power is okay. Bonus points for making the GM snort soda out his nose.

You only ever need to spend one success on style; if you have more to spare, put them into quality.

This file was last modified at 1635 on 06Jan00 by trip@idiom.com.