Damage

Overview

Damage in XCOM comes in two major ways, and then there are some oddballs:

• Weapon (a.k.a. firearm or gun) damage, and
• Explosive damage.

Technically, explosives are weapons. But on this wiki, "weapons" usually means firearms, as separate from explosives - but use your judgement when reading any particular page. Still, on this Damage page and on the Explosions page, "weapons" always means firearms as opposed to explosives, unless otherwise stated.

Past these two types of damage, there are two important target classes: Units and Terrain. (A third target class is objects on the ground.) The application of force to these two targets types is different. A 2 x 2 table follows. Percents mean, percent of weapon strength as shown in UFOpaedia (an important point):

           Firearms   Explosives
Units       0%-200%    50%-150%
Terrain    25%- 75%      50%

Rules:

• For units, armor always reduces calculated damage, before any damage is applied. Units take damage that exceeds their armor and "remember" it, by having their health damaged.
• But terrain is unaffected unless damage is equal to or greater than its health rating, at which point it is simply destroyed. (This is sometimes called terrain's "armor" value, but for terrain, "armor" does not equate to the XCOM soldier sense of armor.) If terrain has not been outright killed by a particular shot or explosion, it stays at perfect health, unless and until some future damage exceeds its rating. Thus, terrain is either obliterated or in perfect health. Just the same, the XCOM programmers designed the game so that if terrain objects are "killed", they usually turn into a "damaged" object. Here's where "melted walls" or "burnt corn fields" come into play. Still, even these latter are terrain objects which, in turn, can be destroyed if damage exceeds their rating. Once the "regular" and "dead" tile have both been killed, once sees raw earth at ground level, or nothing, at higher levels.
• As you can see from the table above, it's important to realize that the UFOpaedia shows average weapon strength versus units. And conversely, both weapons and explosives only impart half their UFOpaedia strength versus terrain. This is a fixed half, for explosives, and half on average, for firearms.

Some units also have modifiers versus particular weapon classes, as shown below.

The less common (but no less fun!) forms of damage are:

• Stun damage, provided by the Stun Rod and Stun Bomb and even smoke. Oddly, the Stun Rod is the lone melee weapon in XCOM, and the Small Launcher's stun bomb follows the rules of explosives for its blast pattern and tile "explosive" strength, but gives 0-200% stun damage at a given tile; see Small Launcher for more clarification.
• Incendiary damage is a complex but ultimately fairly weak type of damage.
• Objects dropped on the ground can only be destroyed by explosive damage, at particular fixed strengths as shown here .

Wise X-COM commanders are mainly concerned about unit damage from weapons - explained in detail below. But see Explosions for more about explosions and terrain.

Formula

 Damage to Unit = (Weapon Damage × Damage Modifier) - Armour 

If the bullet does negative or zero damage, then the bullet is ignored (for damage purposes, but you still get Firing Accuracy experience if it did hit). If the bullet does damage, then there's a chance that the armour plate that it struck will deteriorate by a few points, as shown below.

That's the basic idea. Let's expand on the variables a bit:

Weapon Damage

Weapon damage will be a random number between 0 and two times the damage level of the weapon listed in the UFOpaedia. In reality, all of the damages listed in the UFOpaedia are the averages for the weapons. Note that the doubling of the damage is done before the modifiers are applied.

(edit: In TFTD, the listed weapon damage in the UFOpaedia is still the average damage caused, but the difference from UFO is that random weapon damage is rolled twice and averaged, which produces values which are more often closer to the average)

Damage Modifier

All units in the game will have various modifier levels for all the ammo types in the game. The modifier is simply a percentage multiplier that changes the weapon damage, for better or for worse. For more information, see the next section for specifics.

Armour

The armour section the bullet hit. This can be the front, rear or the left or right side armour for ballistic projectiles. Under armour can only be hit when the target is at or standing right next to the very centre of an explosion from an area-effect weapon, otherwise it's treated as directional damage. To put it bluntly, armour is pure damage reduction.

Damage Modifiers

A damage modifier is a percentage value that alters base damage when calculating damage. Other ways to interpret this include damage multiplier, damage susceptibility, damage resistance, damage vulnerability, etc.

Every unit in the game is assigned an armour class, with each class containing a table of modifiers that determine how well it absorbs the various damage types.

The damage percentages start at 100% for unaltered damage. Values over 100% indicate more damage will be taken, while values under 100% mean less damage is taken.

Susceptible to...

Ammo Type	Damage Modifier Category
	T+I	Hu+	PA1	PS	Tnk	Snk	Eth	Mut	Sil	Chr	Rea	Sec	Cyb	Zom
Armour Piercing	100	100	100	100	100	100	100	60	100	100	100	100	80	60
Incendiary	100	100	80	0	40	70	70	100	0	80	170	100	100	100
High-Explosive	100	100	100	100	75	100	100	100	130	100	100	80	60	80
Laser	100	100	100	100	100	100	100	100	100	100	100	150	100	70
Plasma	100	100	100	100	100	100	100	100	100	100	100	80	100	70
Stun	100	100	90	80	1002	100	80	100	100	90	100	100	100	0
Melee	100	120	100	100	90	100	100	100	100	100	100	100	100	100
Acid Spit	100	160	110	100	40	100	100	100	100	100	100	100	100	100

¹ Due to a bug in the unit spawn routine, Personal Armor gets assigned the modifiers of a Power Suit.
² Tanks cannot be stunned.

Column	Modifier Index	Unit Type(s)
T+I	00 / x00	Terrain and items.
Hu+	01 / x01	Unarmored Soldiers, Civilians, Sectoids, Celatids and Floaters.
PA	02 / x02	Personal Armor.
PS	03 / x03	Power and Flying Suits.
Tnk	04 / x04	Tanks and Hovertanks.
Snk	05 / x05	Snakemen.
Eth	06 / x06	Ethereals.
Mut	07 / x07	Mutons.
Sil	08 / x08	Silacoids.
Chr	09 / x09	Chryssalids.
Rea	10 / x0A	Reapers.
Sec	11 / x0B	Sectopods.
Cyb	12 / x0C	Cyberdiscs.
Zom	13 / x0D	Zombies.

To summarize re: the all important X-COM armor:

• AP, HE, Laser, and Plasma: All types of X-COM armor have full/normal (100%) susceptibility to these types of damage
• Stun: All armour has a 20% resistance to stun damage. (Personal Armour should only have a 10% resistance, but receives the modifiers of a Power Suit due to a bug.)
• Incendiary: All armour is immune to fire damage. (Personal Armour should only have a 20% resistance, but is bugged.)

See Also

• GEOSCAPE.EXE
• Alien Life Forms
• Weapons
• Damage Modifiers (TFTD)

For another way to view the same info above, see this.

See also: TFTD Damage Modifiers

Example

Adapted from Zombie's kindly example:

Scenario: Beginner level Muton mission. Your soldier is carrying a normal Pistol and you want to know what is the chance that a Muton Soldier's front armor will absorb a direct hit without lowering health.

Vitals: 
Muton Soldier front armor = 10
Muton Soldier health = 125
Muton susceptibility to Armor Piercing ammo = 60%
Pistol listed power = 26 (average)

Calculation: 

Max damage for a Pistol against a Muton is lowered due to susceptibility:

 Modified max damage = INT(26 * 2 * 60 / 100)
                     = INT(52 * 60 / 100) 
                     = INT(3120 / 100)
                     = INT(31.2)
                     = 31

where 2 is the max modifier (200% of UFOpaedia listed power) and 60/100 is the damage modifier (60%)

The range of values the Pistol can deal is 0 to 31 points of damage (or a range of 32 different values). The equation's steps are shown because XCOM's math sometimes leads to slightly unexpected values in subsequent steps.

The Muton Soldier has a front armor rating of 10. It will absorb up to this much damage without changing health. In other words, it will negate the first 10 points of damage a Pistol can dish out (0-10; 11 possible values). Since the Pistol has a range of 32 possible values, the probability that a direct hit will be blocked by Muton armor is simply 11 / 32 = 34.4%.

Okay, say you want to know the probability of doing damage to a Muton's health. The pistol still has 32 values, but instead of absorption we want penetration. 10 points of damage is absorbed, so we need at least 11 to penetrate. 32 - 11 = 21 values which will breach. 21 / 32 = 65.6%.

21 is also the maximum number of damage points which might be deducted from the Muton's health. Assuming the Muton was initially uninjured, in the worst case (for him!) he will have an ending health of 125 - 21 = 104.

On average, there will be 15.5 damage dealt (0-31). Then armor (10) reduces this to an actual (penetrating) average damage of 7.22. (It's not simply 15.5-10=5.5 because initial damage that's less than ten becomes zero penetrating damage, not negative penetrating damage. The removal of these negative values causes the expected average to rise, as it were.)

If you need precision while testing, note that the game applies truncation after making its damage roll. It does not first determine the maximum (including damage modifiers), and then roll randomly/evenly from 0 up to the maximum, per se. To wit: if you hack a pistol to an average damage strength of 1, there would not be an overall roll of 0 to a maximum of 1 (with average damage of 0.5) as might be implied from the Muton-versus-AP example above. Instead, there is a roll of 0, 1, or 2, to which the .6 modifier is applied. Only a roll of 2 results in non-zero damage (INT(2x60/100)= INT(1.2)= 1), and the Muton only takes an average of 0.33 damage, not 0.5. Usually this effect is insignificant relative to the large damage values found in the game, but it could matter in testing situations involving very low damage strengths. It also means you need to take into account all possible values versus individual truncation effects, if you want an ultra-precise listing of e.g. how often armor is breached.

Armor vs. Health Damage

When there is penetrating damage (i.e., damage is >0 and not all blocked by armor), Health and Armor Damage have a very simple relationship:

 Health Damage = 10 * Armor Damage, minus 1 to 10

Or the other way around:

 Armor Damage = INT( Health Damage / 10 ) + 1

In table form:

Armor  Health Damage
Damage   Min  Max
   0      0    0
   1      1    9
   2     10   19
   3     20   29
   4     30   39
   5     40   49
   6     50   59
   7     60   69
   8     70   79
   9     80   89
       etc.

Of course, this assumes armor is not zeroed out by the hit. Also note that you will always have armor damage if you have health damage and vice-versa, if there was damage penetration. Stated another way, you will never have armor damage if you don't have health damage (i.e., when there is insufficient damage to breach the armor).

You will see this health/armor relationship if you watch damage from individual hits. However, the relationship is muddied if you only look at a unit after a number of hits (or, of course, if armor is broken through). The most extreme example would be if a unit were hit with e.g. five hits of 1 penetrating damage point each. The unit would have 5 health damage and 5 armor damage, which would appear contrary to the above table.

This relationship has been been tested for a wide variety of explosions and some light weapons vs. Mutons, and some hits on soldiers. It has not otherwise been widely tested, but is presumed true unless/until found otherwise.

As stated, the above is for damage that penetrates. It is possible for hits (guns or explosions) to do zero damage. This happens on the rare occasion that a weapon damage roll is actually zero, or, much more commonly, when armor has blocked all the damage. You still get an experience point toward Firing Accuracy if damage fails to penetrate. You only have to hit the target(s) to get Firing experience; there doesn't have to be damage.

For Health Damage versus Fatal Wounds, see Fatal_Wounds#Probability_of_Fatal_Wounds.

See Also

• Weapons
• Explosions
• Firing Accuracy
• Health
• Medi-Kit
• Experience