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Dice combat resolution systems

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Joined: 12/01/2008

I'm trying to come up with a clean combat resolution system.
Part of the problem is that I've seen relatively few systems and therefore lack the experience to compare them and build from them.

Is there are resource out there that perhaps catalogs various mechanics?

Part of a personal challenge to me is that I tend to design overly complex mechanics and then try to simplify them. Sometimes high complexity can work, but if there are many other parts to the game, it quickly becomes the bottleneck.

In a previous game (fantasy strategy), I had roughly company sized military units.
Attributes included: separate attack and defense scores, range, movement speed and type (mounted, flying, etc.) magic attributes, armor attributes, supply cost, etc, etc.
In other words, a fairly high level of detail.
But, since this was the main focus of the game, it was probably justified.

To determine a battle outcome, you would roll 2d10 + your attack score for a particular unit. To hit a unit, you would need to roll the target's defense score or higher. (There are some other modifiers, but that's the basic mechanic)

However, in a new game I'm designing that level of detail is not wanted. First, the units are battalion or brigade sized. Second, there are other parts of the game that need more focus.
I want to reduce the combat strength to a single number.
But I still want to represent the idea that:
• A tank unit is tougher than an infantry unit (both damage it can deal, and damage it can absorb)
• Battles between equal units should take roughly the same time as battles with differently strengthed equal units. (important for other play issues)
• There is some granularity in the attrition rate to give the waring sides a chance to gauge the battle and retreat if necessary. (not all or nothing)

Originally, I had each unit have an attack value and an armor value.
On a d20, you would have to roll (your attack value - target's armor), or lower to score a kill. Additionally, some units got to roll additional dice, and some got and additional hit before dying. Most needed rolls would be less than 8, many even lower. This provided attrition granularity.

This worked balance-wise but was still too complicated.

So, I dropped the additional hits and dice, and tried to represent than in an increased combat score.

I though about rolling (your combat score - your target's score) or lower to hit, with 1 always hitting and 12 always missing.
That lead to some strange results (equal units were the same as units with a 1 point difference) and in many cases the battle took too long to resolve (needing 1 or 2 on d10.
Then I though of subtracting only half the targets combat score. But that seemed messy and suspiciously close to having two separate combat values again.

Here's what I'm currently thinking.
Each unit decides to attack a specific unit in the battle and rolls a d12. Normally, a 1-6 hits, 7-12 misses.
But this will be modified based on the relative strengths of the units to each other.
For every point below your target's score, you subtract a point from the numbers that can hit.
For every point above your target's score, you add a point to the numbers that can hit.
A roll of 1 always hits, and a 12 always misses regardless of the needed roll.

So in a battle with a 6 vs. 7, (difference of 1)
The 6 strength would need a 1-5 to hit
And the 7 strength would need a 1-7 to hit
(These odds are the same for all battles with a difference of one point)

So, any battle between units with a difference of two means that the stronger unit is twice as likely to hit.
A battle between units with a difference of four means that the stronger unit is five times as likely to hit.
Scores don't represent an absolute value, but rather a relative value to any given opponent.
So 2 vs. 4 is equivalent to 10 vs. 12

This system will give six different possible odds in a battle.

I originally tried this with a d10 (hit on a 5 or lower) but found that the range of odds was limiting. And that a difference of only 1 point made for too decisive of an advantage. And I felt that the low amount of possible rolls meant that there was too much uncertainty.

My next thought was to use a d20 (hit on 10 or lower) and change combat scores accordingly. (Also 1-2 always hit, 19-20 always miss)
This would allow introduction of minor differences in strength; a difference of 1 point would only yield a 10% advantage.

But somehow, using a d20 seemed a bit unwieldy, and seemed to take a bit longer to compute your hit roll, and a bit longer to read the number rolled. But maybe that's just me.

I think the best would be a d14 (hit on 7 or lower), but they are much more expensive than other dice ($5 apiece!)
So I'm compromising and using a d12 right now. But for some reason they seem to take an unusually long time to stop rolling, more so than even a d20!

So, what do you guys think of such a system? It seems pretty straight forward to me, but do you see it as too complex?
Do you see a complexity increase with the increase in the die faces? (d12 vs. d20)
Perhaps you know of a different mechanic that I should consider?

Also, let me know if you need me to describe some typical units or a typical battle in more detail.

Joined: 12/31/1969
Dice combat resolution systems

You might want to consider a modified Axis and Allies type thing. It can be modified to take damage and hitpoints into account quite easily.

Joined: 12/31/1969
Dice combat resolution systems

Ugh. It sounds like trying to figure out Thac0 back in 2nd edition DnD! :P The numbers and mechanics seem fine, though. It's a good concept. I imagine you wanted the d14 to allow for 1=hit, 14=miss and 2-13 are the normal range?

Joined: 12/01/2008
Dice combat resolution systems

NetWolf wrote:
Ugh. It sounds like trying to figure out Thac0 back in 2nd edition DnD! :P The numbers and mechanics seem fine, though. It's a good concept. I imagine you wanted the d14 to allow for 1=hit, 14=miss and 2-13 are the normal range?

Wait, I'm confused. You first said Ugh, and then said it's good. Can you clarify? Do you mean Ugh to the first game, and good to the second game?

The reason I think d14 would be nice is because there is a greater range of odds possibilities, while not being as "numbery" as using d20. Also, a greater range means better fidelity for the first few odds ratios. And this seems desired.

On a d10, a 1 point difference yields a 3/2 advantage in battle outcome. 2 points gives greater than 2/1 at 7/3. That seems quite high, and not enough options in beetween.

d12 gives 7/5 odds for 1 point advantage, 2 points is 2/1. Perhaps still a bit high, but playable I think.

d14 gives 4/3 for 1 point, 9/5 for 2 points, and doesn't breach 2/1 until 3 points difference at 5/2 odds.

d20 gives 11/9 at 1 point, 3/2 at 2 points, 13/7 at 3 points, etc. I don't think all that much detail adds much value from d14, and so it is wasted complexity.

So, d14 seems like a good mid-range value.
But yes, 1-7 hit, 8-14 miss, are the base values. And 1 always hits, and 14 always misses.

rellekmr wrote:
You might want to consider a modified Axis and Allies type thing. It can be modified to take damage and hitpoints into account quite easily.

Actually, Axis & Allies was may starting point (for the newer game). The limitation in Axis is that a unit had the same chance of hitting opposing infantry as it did going up against opposing tanks. I want to reflect that tanks are also harder to kill, not just more damaging.

Furthermore, in Axis you'll notice that the units have both an attack and defence score. (though only one is used at a time) I'm hoping to confine the combat score to just one number in my effort to simplify. Again, I originaly had additional hit points if my first draft of the new system, but I removed it to make things more streamlined.

I'm not opposed to bringing back a defence or armor score, but I hope to resolve this without adding more numbers if I don't need to.
I'm noticing, however, that removing complexity in one area can have the effect of increasing it in another area if I try to retain unit interactions.

In this case, removing hits and defence scores makes the player have to do a bit of math to resolve combat. I don't think figuring out how far apart your scores are is a huge burden. Perhaps subtracting that from your needed hit roll is getting there though?

Though in requireing even a tiny bit of math, I feel like a little bit of elegance has been lost somehow. But maybe I'm worrying about it too much.
What do you think?

Joined: 12/31/1969
Dice combat resolution systems

Look at how much time each roll is gonna take to resolve. Then look at how many rolls are gonna happen per game. If one goes up you have to reduce the other or the game will spiral out of control.

Joined: 08/26/2010
Dice combat resolution systems

OK, since you are willing to work with out of the ordinary die, (never knew there was a d14) would you work with multple types of die in the same game? Here is something that I tried when I was designing my first "war game" if you will. I was looking for groups of 4 units of the same type(lances to borrow from Battletech/Mechwarrior) to fight at the same time, so roughly squad type combat. It seems to work well, but then again I've only gotten to play it twice so far, just didn't stay high on my list for playtesting, although I hope to get back to it soon.

unit - (will show 2 as example)
def value - (meet or beat)
attack die - (#of die rolled equalled unit strength, 1-4)

Armored infantry
d4 / d4-1
3 / infinite
take over cities / bases

heavy armor
d8 / d4
8 / infinite

of course there was stuff all inbetween, light and med armor, choppers, recon, and all were placed on a simple chart to track how strong a unit was, you started w/ a strength of 4 (roll 4 att die), any scored hit reduced the opposing unit's strength by one and as that went down you just rolled less die for att. I wanted it to be more about the offense so I actually made the defenders in any combat subtract 1 from whatever they rolled from each die (makes inf worthless as defenders, but they make up for it by being the only types of units to take over cities and hell, they were cheap!)

just a thought, but I found this system to be fairly painless, the only prob happens if you don't want to use any type of tracking sheet for the strength of the unit and what ammo they have left. Really wouldn't work then.


Joined: 12/20/2010
Dice combat resolution systems

there's a d14?

Joined: 08/26/2010
Dice combat resolution systems

I was suprised too, if you google for d14 dice you'll see it, just a smoother d10 really, cool though.


Joined: 12/01/2008
Dice combat resolution systems

Sen wrote:
there's a d14?

Yes, and a d16 and a d24, and many other unusual ones too.
d24 may have some interesting uses because it can correspond to hours in the day, but that's another story.

The downside is that where more common dice cost <$.50 and less common ones like d12 may cost as much as $1, it seems that d14 cost $5 apeice!

Presumably because places don't make too many, as I can see any technical or fabrication reason for the high price.

Interesting system, I like some of the ideas there. It's a bit more detailed than what I'm after. Though you've given me some things to mill about for other games. Again, having a seperate deffence score and a seperate dice stat is effectively going the two combat numbers route.

I'm still hoping to get a satisfactory result with less.

For comparison, here is what each military unit would have for stats on the playing peice (cardbord counter).

Unit Name: Probably named after the primary fighting element.
Though, a unit can be thought of comprising numberous other support vehicles/elements. Mobile logistics depots, limited air defence squads, anti-armor squads, scouts, ect.

Movement Points: For aerial units this would instead be an operational range.

Combat Score: A value representing an overal combat strength.

Attack Range: Most units won't have to worry about this as a single battle can represent various military engagements between warring units. As such, range is not needed because combat represents a general military action over the course of a month. (1 game turn)
Range would instead be relavant for a long range strike unit/missle base that could strike units in neighboring spaces. These units will likely not be able to participate in normal combat rounds. (except maybe as a single opening strike)

Environment: An element showing which envorinments the unit can operate in. On the reverse side of the counter is a seperate set of stats showing how the unit operates in certian unfavorable environments.
This is a space conquest game. As such, there are different planetary envoronments to consider. A unit that is effective on one planet may be poorly suited for another - if it can even conduct operations there.

Cargo Capacity: For those units that can carry other units. Like transports or carriers.

Picture: A graphic showing a silloutte and maybe a nato-like symbol. The unit symbot will also provide information as to what type the units is. Surface vessel, aerial unit, missile base, infantry, etc.

Cost: Cost to produce a unit. This value will not appear on the counter and has no bearing in combat.

Your point is well taken, and I'm trying to make sure combat doesn't take too long.
That's one of many reasons I want things to stay simple. And also why an earlier combat mechanic was dropped. It had too many instances where both units needed a 1 or 2 on a d10. It just took too many rolls to get hits.
Under the current system, at least one unit will always have at least a 50% chance of hitting.
Plus, I don't think there will be many extended battles. You won't see players controlling hundreds of units. More like a couple dozen scattered across different worlds.

Joined: 08/26/2010
Dice combat resolution systems

Glad I could stir up some thoughts.

For comparison, here is what each military unit would have for stats on the playing peice (cardbord counter).

I can understand that being alot if you're going to put it all on the counter. On mine I just put the pic (same units have different pics for each army) on the front and then the Army's insignia and a number on the back, as players can have up to 6 of any type of unit on the board at one time. All of the other stats go on the tracking sheet, below is a chunk of one

That is a quick look, on the full sheet there is a row of five for the tracking of strength and ammo, and 5 types of unit print out on a single sided page. We think along the same lines for range, except for my "missile/artillery" units, the units must be in an adjacent square on the board, I used squares intead of hexes b/c I didn't care about facing, they aren't single unit combats (at least at first) Tried to keep it simple, as a side note I hate the way stuff from power point transfers to bmps and such, guess one of these days I'll have to learn a real graphics program...... until then though... =)


Joined: 12/31/1969
Dice combat resolution systems

Hehe. The Ugh was the memory of Thac0, not your game. If you look at the percentages that the d14 and d20 represent, you should probably just use the d20. If for no other reason than availability.


2-7: Hit Range
8-13: Miss Range
14: Miss

-each point is roughly 7%. That means that a +2 bonus would grant a +14% chance to hit.



1: Hit
2-10: Hit Range
11-19: Miss Range
20: Miss

-Each point is 5%. A +2 bonus grants a +10% bonus. Still a sizable bonus, but compared to the d14 it's a reasonable bonus.


Let's look at it in a functional use:

"Generic Tank"
8 Combat

"Generic Troop"
4 Combat

The Tank gets a +4 bonus when attacking the troop. On a d14, this would change their hit range to 1 to 11, making 12-14 a miss. That gives the Tank a 77% chance to hit, total.
If the Troops were to attack the tank, they would subtract 4, making their hit range 1 to 3: 21% chance to hit.

Now let's look at the same stats with a d20. The tanks +4 bonus is still a sizable 1-14 hit range, making it a 70% chance to hit. The troops have a 1-6 range, or a 30% chance to hit.

While the d20 weakens the tank a bit, it also makes the troops somewhat useful, even against armored vehicles like the tank. If you wanted to balance it out a bit you could even add in an "Armored" bonus that grants an additional +2 bonus to defense.


From a marketing standpoint, you need to make it both appealing and accessable. Most gamers will have a d20 or at least access to d20. If you make the players use a d14, it not only makes it difficult to acquire, but also less customizable. Let's face it, some people get addicted to dice and want a variety of colors, patterns, and shapes. It's much easier to get hooked on a cheap die with a wide variety of colors than it is to get hooked on a die that costs $5 a pop.

Not only that, but if this game is ever marketed, the cost of the die will (likely) cost half as much as the cards themselves. Unless you plan on having the dice made specifically at the same time as the cards, this will up the cost of the game. If the die isn't provided, why utilize a die that will send $5 to another company, when that money could be spent on your cards. If they only spend $0.35 on a d20, that means they have plenty left to spend on a booster pack! ;)

Sure that may be a ways away, but it's still a consideration.


Joined: 12/01/2008
Dice combat resolution systems

Ok, so I'll count that as a vote for the d20.

The cost of the d14 is made even worse because you'll need a few of them if you want to roll them all at once. (To keep combat quick)

Battles will frquently occur between multiple units at once.
This is also how you overcome a powerful unit, you atttack it with more troops.

If I move to the d20 version, I'll likely have to re-balance the unit numbers.

In your example, the 4 power Infantry vs. 8 power Armor seem to make the infantry useless against the armor company. My feeling is that it should be quite a mismatch.

But now if three infantry companies were to fight the armor unit at once, you'll notice the odds quickly start to favor the infantry.
Even if the tanks manage to kill one infantry every combat round, the infantry units would end up with five chances to hit the tanks just once and win the battle. Or a chance to pull off a tie on the sixth roll.

So, infantry isn't usless, you just need more of them to take out a strong unit.

Anyway, did I actually post Infantry 4, Armor 8?
I don't rember doing that, but that's exactly the numbers I was using.
Well, that's for the basics. There are ways to build higher tech, and more capabile infantry and tanks too. A better armor company might be combat value 10, better infantry might get a 6. (Don't forget there are out of evironment numbers to weaken units too.)

The worst disparity in value at the moment is 4 vs. 12. Right now all infantry is considered mechanized infantry. If I add some militia or infantry without access to APCs then there will be yet a smaller value.

Let's see how this plays out on a d12...
Low tech infantry company: 4
3rd generation armor company: 12

I imagine this would be like a modern company of M1A2 Abrams going against WWII G.I.s

One on one, the armor unit will clobber the infantry. No question about it. But, there is still a small chance for an upset. (at .7% of the time)

But if there are four times as many infantry units, the situation changes drasticaly.
I ran the battle twenty times with no retreating, and here are the results:
Infantry wins: 12 times
Tie (all killed): 1 Time
Armor wins: 7 times

The infantry won almost twice as many times, but not without losses. In only one battle did the infantry win without losing a single unit.

It should be noted that this example is overkill on d12. Fighting vs. a 10 strength unit gives the same odds. If this was d14 there would have been slightly worse odds.

So, how does a unit that is so outclassed manage to defeat a superior attacker? Overwhelm them with numbers. Conceptualy, it could be imagined that there's just to many targets for the tanks to cover. Even though the tanks are practicaly invincible on the battlefield, the numerous infantry are overrunning supply/command bases and the tanks are hitting their endurance limit, exausing their fuel, ammo, and failing due to shortage of maintinece.

So having many units is a sure way to get an advantage. Aha! but population need to run, well, everything from manufacturing to military units, is one of the most valuable resources in the game. And how to use that population needs to be carefuly considered.

Do you want to use that population to slowly build up manufacturing and resource centers so you can produce 3rd generation tanks? Do you even have acces to the respources to do so? Or use them to build quick weaker troops to throw at beefy attackers? Does the planet's evvironmental conditions favor you or the enemy? Maybe those 12 power tanks would be fighting at power 8 on this planet. That gives you time to hold off an attack with weaker troops while you build other plans.

Lots of strategic decisions to be made here.

A slight nitpick:
You wrote each point on a d20 is 5%, so +2 grants +10%
I think you meant the right thing, but wrote it wrong.
A +2 advantage actually yields a 4 point spread, or 20%
A +1 advantage would give a 2 point spread, or 10%

Joined: 12/31/1969
Dice combat resolution systems

Nope. The 4 Attack infantry and 8 Armor tank were just random units I threw out.

I must have missed the part where every point difference yields a +2/-2 bonus to the spread. I was basing my stats off of a standard +1 advantage = +1 to the roll.

What ever die you decide to use I would also consider the maximum attack/armor total you plan on using. You mentioned an Armor 12 unit.....that seems like a bit much, especially if you use a d12 as you did in that example. That really instigates the exact issue you were trying to avoid: forcing a player to only be able to hit on a "1".

With the d20 example, I would limit the maximum armor/attack to 10 since that would effectively make the unit invulnerable to lower value units, but still fairly even against those closer to it's own value.


About multiple units engaged in a single exactly are you working the mechanics for this? It looks like the Infintry you used as an example was able to combine their combat scores into a single strike, but were also picked off one at a time by the tank.... If I understand that correctly, the example you gave would give the Infintry a +4 bonus over the tank (A +8 spread?), thus making even three Infintry equal to a single tank, though they constitute 3 targets rather than one.

Joined: 12/01/2008
Dice combat resolution systems

NetWolf wrote:
I must have missed the part where every point difference yields a +2/-2 bonus to the spread.

A 1 point difference yields a 2 point spread because the lesser unit will subtract 1 from the range, and the greater unit will add 1 to the range.

Oh, I see what you did wrong. Don't add/subtract values to the roll itself, rather the spread modifies the numbers that hit/miss.

For example, on a d12:
1: Automatic hit
2-6: Base range to hit
7-11: Base range to miss
12: Automatic miss

Infantry: 4
2nd Generation Infantry: 6

In an example of a 4 vs. 6, the numbers would change thus:
4v6 is a difference of 2. So for the Infantry, which has a lesser score, his range would look like:
1-4: hit (2 less than the base value of 6)
5-12: miss

The 2nd Generation Infantry, with the greater score, would look like this:
1-8: hit (2 more than the base value of 6)
9-12: miss

So, the 2nd Gen. Infantry has a 2/1 advantage over the regular Infantry.
They have superior equipment, weapons, recon, mobility, etc.

I say 2/1 because the 2nd gen infantry has twice as many chances to hit, but the outcome probabilities would really break down like this:
11% 2nd gen. infantry killed, regular wins
22% both units killed
44% regular infantry killed, 2nd gen wins
22% no units killed - initiate a new combat round if no retreats
Total 99% due to rounding errors

So on a d12 a 2 point difference is a decisive advantage.

The addition of a second regular infantry changes the situation quite a bit.

Two regular Infantries vs. one 2nd Generation Infantry.
15% No hits - initiate a new combat round if no retreats.
29% One regular infantry is killed, 2nd gen infantry unharmed - initiate a new combat round if no retreats. (with one less reg. infantry)
37% One regular Infantry is killed, 2nd gen infantry is killed - the surviving regular infantry wins the battle.
19% Regular Infantries are unharmed, 2nd gen infantry is killed - the regular infantries win the battle.

So with twice as many troops, the regular infantry wins the battle 56% of the time on the first round of combat. 29% of the time the odd will continue in the 2nd gen infantrys favor as in the first example, 15% there is no change in the battle odds.

I guess I should explain how a combat round works at this point.

When units try to move into a space occupied by opposing units, and battle will be initiated.
1) Opportunity for any units to retreat
2) Remaining units enter battle
3) Each unit gets one die roll, and gets to decide where to direct its firepower. The necessary roll is dependant on who it decides to attack. (compare scores) Combat is considered to occur simutaneously. Make all rolls before moving to the next step.
4) If a unit has been hit, it is killed and removed from the battle.
5) Goto step 1

I may add a terrain modifier for the defending units, especially if I move to the d20.

As far as the issue of only being able to hit on a 1... It's not necessairly bad by itself. It's bad when BOTH sides can only hit on a 1, as the battles take too many rolls.
In the current system this does not occur.
In fact, for every unit that needs a 1, another unit hits on 1-11

Joined: 12/31/1969
Dice combat resolution systems

I see what you mean now. You were tabulating both the bonus to the stronger unit and the penalty to the weaker unit at the same time! :P

Now that I understand all the rules of combat (Including simultaneous combat rolls), I have to say that it looks like a pretty good mechanic. I would still suggest using a d20 for value, if nothing else.

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