Damage calculation

Damage of a weapon in Gladius is calculated by multiplying the of one shot with the number of  and the number of copies of the weapon. However, if the total number of attacks is less than the amount of members in the squad you're firing at, then the damage will be capped at the health of as many squad members as you have attacks. For example, if a Predator were to fire at a squad of Guardsmen with it's single Lascannon, the Lascannon's damage would be capped at 2 because that is the health of one Guardsman. After this, the capped damage will be multiplied with the weapon's, the target's (inverted and modified by ) percentage and with any potential  effects.

Effects like Blast, Large Blast, Template, Mourning Blade of Lazaerek are a special case in how they modify damage. They multiply the capped damage by a certain amount of alive squad members in the target. Alternatively you could say they increase the damage by the health of a certain amount of alive squad members. For example, Blast increases the damage by the health of 1.5 additional squad members. That means the capped damage will be multiplied by 2.5, as long as there are at least 3 alive squad members in the target. If there were only 2 members left in the squad, then Blast would only multiply the capped damage by 2 and if there's only 1 model in the target, Blast would not do any bonus damage.

Damage Reduction
There are a couple different types of effects. 'Ranged', 'hero', 'invulnerable', 'city', 'feel no pain' and 'witchfire'. They are obtained from terrain, items, actions and traits. Ranged and witchfire damage reduction only apply to ranged and witchfire attacks respectively, but all the other damage reduction types apply to all attacks.

Note that multiple effects of the same type might not always stack. If your unit benefits from a and a, then only the higher one is taken into consideration.

Armor and Accuracy
Armor and accuracy modify damage by multiplication. A weapon with accuracy 6 (50%) will actually only do half its displayed damage. When firing at an enemy with armor 6, the damage would be halfed again. Every point of reduces the target's armor value by 1 for the attack.

Every point of armor or accuracy increases their effect by about an additional 8%. The maximum damage reduction you can get from armor is 83%, which is reached at armor value 10. It is still possible to increase armor beyond 10, but it will only serve to counter potential armor penetration. Accuracy can be increased beyond 100% and will start increasing damage instead of reducing it.

This chart shows the percentages at the values 0-12.