Mass combat rules

Mass combat rules

There are a lot of different mass combat systems that have been put out for D&D over the years, some official and others custom rules. These range from systems that are very technical and have variable scalability for any size of mass combat, to those that are virtually devoid of dice rolling and are more story oriented, and others who base is so far from D&D that they may as well be a separate game system.

My intention is to create a system of rules that keeps the spirit of D&D in place (D20 system), allowing the characters to use their existing skills, feats, and attributes to affect the outcome of the battle, while also reducing the clutter of die rolling and DM overhead when dealing with hundred or thousands of units.



Choose a scale that is easy to work with. Too many units and combat can take a long time. Too few units and combat becomes a simple statistics game.


A unit is only as good as it’s weakest link.

The unit stat block

Unit’s are generally a homogenous grouping of the same or similar type of individuals. It is a simple way to represent a group of individuals with similar capabilities. If the capabilities of the individuals are vastly different, it can cause issues with the abstraction and cause weird results.

Name of unit: Regular Militia
Scale: 15ft
Size: 1×1
Number of Individuals: 9
Unit HP: 117
Individual HP: 13
Morale: +1
Race: Human
Class/Level: Fighter / 1
Init: +1
AC: (chain shirt, heavy shield, dex +1) 17, touch 11
Saves: Fort +4, Ref +1, Will +0
Move Rate: 4 squares
Melee: (longsword) num of att. 3, attack bonus +3, damage 5.5 (4.5 +1 str)
Ranged: (shortbow) num of att. 9, attack bonus +1, damage 3.5 (1d6), range inc. 60 ft.
Feats: Weapon Focus (longsword)

Unit HP

The total of each every individuals HP in the unit

Individual HP

The total unit HP divided by the number of individuals in the unit

Morale Modifier

  • Every 4 months of training +1 (no more than +3)
  • For every battle the unit has been in +1 (no more than +5)
  • Unit is composed of chaotic creatures –1
  • Unit is composed of lawful creatures +1

Unintelligent creatures and those under direct mind control do not have a morale value.

Initiative Modifier

The initiative modifier is the lowest modifier for any of the base individuals in the unit.

Armor Class

AC is the average of AC for all the units in the group. Add all the AC values together and divide by the number of individuals in the unit.


The saving throw value for Fortitude, Reflex, and Will Power are the lowest value for any particular individual in the unit.

Movement Rate

Is generally double the movement rate of the slowest individual in the group, divided by scale rounded down. Refer to the movement section below.

Melee Attacks

Number of attacks is the total full round melee attacks each individual has, then squared (round down). For example a unit of 10 first level fighters (1 attack each) would be 1+1+1+1+1+1+1+1+1+1 = 10 then √10 = 3.16 rounded down = 3. The bonus to the attack roll is the lowest of first attack for any of the units in the group. Damage is the average damage of all the melee weapons.

If the unit is equipped with reach weapons (polearms) multiply the number of melee attacks by two.

Range Attacks

Number of attacks is the total full round range attacks each individual has. Attack bonus is the lowest for any unit in the group. Damage is the average damage of all ranges weapons.


Heroes are treated as points on the map and move and act separately unless joined to a unit. When a Hero is joined to a unit (this happens automatically if the player wishes it and the point is moved within the unit’s square) this allows them to use their


Renown is a special stat for PCs, heroes, and leaders. It denotes a characters known success with battle. It’s a score from -3 to +3 added to many of the mass combat checks that a unit makes when a character with renown is embedded and leading a unit.

Everyone starts with a zero renown. Success in leading a unit in battle through an adventure (Unit never scattered, unit total casualties less than 50%, and achievement of objectives) increase a characters renown by 1. Conversely, a failure on all three of these can drop your renown by 1. As a general rule of thumb with NPC’s each five levels equates to one point of renown.

Granting of a renown point or taking away a point is completely at the DMs discretion.

Order of play

Combat is resolved in rounds. Each round starts with any necessary morale checks and rally roles. Then follows the first optional attack round (typically ranged attacks), then movement, followed by a second round of attacks for those who did not participate in the first round. Finally casualties are tallied and the round begins again.

  1. Initiative
    Morale Check
    First Attack
    Second Attack


Roll a d20 for each unit and add its initiative modifier plus any renown bonuses. Each round segment is resolved simultaneously, with each unit performing its action in reverse initiative order.

Morale Check

A unit must make a morale (Willpower + morale bonus + leader renown) check when any of the following conditions happen:


If a morale check is failed, a unit will not attack and will disengage during the move phase. It will continue to leave the battlefield as quickly as possible. Once per round an embedded unit leader can attempt to rally a unit by making by making a Charisma check modified by character renown (+2 if the character has the leadership feat), with a target DC of the failed moral check.

PC’s do not have to flee with units they are attached to, but cannot rally them if not embedded. A unit that fails to be rallied for two rounds in a row scatters and can no longer be rallied.


There are two combat segments in each round. Generally, units can only attack in one of these rounds, the unit leader getting to decide which one. Some units with special feats may participate in both rounds.

Number of hits is 10 + attack bonus + leader renown divided by opponents Armor Class multiplied by the number of attacks rounded down. For example, if the attack bonus is plus 2 and the opponent AC is a 15 and the number of attacks is 10, then the total number of hits is [(10+2)/15]*10 = 8 hits.

If the number of attacks a unit has is five or less, instead of adding ten, roll a d20 for each attack.

Damage is the total number of hits times the damage. In our example if the number of hits was 4 and the average damage 6.5, then the total damage is 26.

A single hit cannot do more damage than the Individual HP. So if a single attack average is 12 points, and the Individual HP is 11, each hit can only do 11 points of damage. This can be exceeded with feats such as cleave, tail sweep, etc…

Subtract the total damage take from the Unit HP. A unit automatically disbands (no morale check and no rally opportunity) if it’s HP drop below zero.


Moving through different terrain has different costs, as shown below. If a unit cannot spend the required number of movement costs to enter a square, they instead pay what they can each round until they have entered a square, but count as being in their old square until that time. The costs are below:

* Light forests: counts as 2 squares of movement
* Heavy Forests/Jungle: counts as 3 squares of movement
* Ruins/Very Rocky: counts as 3 squares of movement
* Building: counts as 3 squares of movement
* Down a Slope: 3 squares count as 2 squares of movement
* Up a Slope: counts as 2 to 4 squares of movement, depending on grade
* Swamp: counts as 4 squares of movement
* Sand or Rocky Desert: counts as 2 squares of movement

End of Combat

Recovering Casualties

Unit Hit Points do not track actual deaths in a unit. They are more a measure of its ability to keep fighting through individual death, injury and surrender. At the end of each combat, a percentage of the lost hit points may be automatically recovered as those injured are helped, those who ran come out of hiding and the death toll is finally tallied.

At the end of battle, the victor (those in possession of the battlefield) may regain 50% (round down) of a unit’s lost total Hit Points back. The loser may regain 25% of a unit’s lost total HP back.

These percentages are modified as follows:
Cleric with healing spells present: +2% per level per cleric (max +10%)
Character with Heal skill rank 4 or greater present: +1% per character (max +10%)
Unit HP dropped to zero: -25%

Disbanding a unit

Any unit with less than 75% of their max Total HP is considered dysfunctional and needs to be reinforced or disbanded. Divide the current total HP by the number of individuals (round down) to determine how many healthy individuals are left.

Mass combat rules

Illians Crossing joescheirich joescheirich