Damage

Or, how much damage can a weapon do to a unit with so much armour.

Formula:

damage to unit = (weapon damage * damage modifier) - armour

If the bullet does negative or zero damage, then the bullet is ignored. If the bullet does damage, then there's a chance that the armour plate that it struck will deteriorate by a few points.

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

armour: Is simply the value of the armour section the bullet hit.

damage modifier: 0.5 if the unit resists and 2.0 if the unit is weak against the weapon's damage type. I'm not sure, but there's probably also a 1.0 for units that neither resist nor are weak against the bullet type.

weapon damage: Weapon damage will be a random number between 0 and the damage level of the weapon. In reality, all weapons do half their listed damages on average (something to do with the distribution of random numbers leaning more towards the middle of the normal distribution curve).

A critical hit is therefore anything above 50% to 100% of the listed damage (or 100% to 200% for double damage, 25% - 50% for units that take half damage).

It's interesting to note that X-Com units take double damage from practically every major weapon type. I know for sure that they take double damage from AP, Plasma and laser (I tested: rifle bullets were doing up to ranges of 60 points of damage to X-Com units when they're only supposed to do 30). No wonder your units drop like flies. At least this is true for unarmoured soldiers. I'm not too sure if armour helps reduce this to normal damage.

-- NKF, Dec 18 2003, reposted by --JellyfishGreen 16:01, 21 Apr 2005 (BST)

Modifiers

Basically, everything's 100% except the following:

Vulnerable to...

Incendiary:
    Reaper:             170%

High-Explosive:
    Silacoid:           130%

Laser:
    Sectopod:           150%

Melee:
    Unarmoured Soldier: 120%
    Civilian:           120%
    Sectoid:            120%
    Celatid:            120%
    Floater:            120%

Celatid Acid Spit:
    Unarmoured Soldier: 160%
    Civilian:           160%
    Sectoid:            160%
    Celatid:            160%
    Floater:            160%
    Personal Armour:    110%

Resistant to...

Armour-Piercing:
    Cyberdisc:       80%
    Muton:           60%
    Zombie:          60%

Incendiary:
    Personal Armour: 80%
    Chryssalid:      80%
    Ethereal:        70%
    Snakeman:        70%
    Tanks:           40%
    Power Suit:       0%
    Flying Suit:      0%
    Silacoid:         0%

High-Explosive:
    Sectopod:        80%
    Zombie:          80%
    Tanks:           70%
    Cyberdisc:       60%

Laser:
    Zombie:          70%

Plasma:
    Sectopod:        80%
    Zombie:          70%

Stun:
    Personal Armour: 90%
    Chryssalid:      90%
    Power Suit:      80%
    Flying Suit:     80%
    Ethereal:        80%
    Zombie:           0%

Melee:
    Tanks:           90%

Celatid Acid Spit:
    Tanks:           40%

"I find it amusing that Celatids are vulnerable to their own spit" -- Danial